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Protect our European outdoor bronze monuments, Good Practice Guide, Culture 2000

  • Haute Ecole Arc, Neuchâtel, Switzerland
Edited by Christian DEGRIGNY
(Greetings by the Mayor of Athens, Greetings by the Minister of Culture)???
Introduction Urban planning for the protection of outdoor monuments
CHAPTER 1 The meaning of outdoor bronze monuments to European citizens
1.1. Social and historical aspects
1.2. The Bronze monuments in Athens
1.3. Bronze sculptures in Göteborg – kings and fighters, water and shipping - donations and
the art for everybody
1.4. The importance of outdoor bronze monuments in Munich
CHAPTER 2 The construction of an outdoor bronze sculpture
2.1. The lost wax process
2.2. The sand-casting process
2.3. What is bronze?
2.4. What is patina?
CHAPTER 3 Deterioration of outdoor bronze monuments
3.1. General principles on the corrosion of copper based alloys
3.2. What factors affect the deterioration of outdoor bronze monuments?
3.3. Problems that face outdoor bronze monuments
CHAPTER 4 Conservation strategy
4.1. General approach
4.2. Case studies
CHAPTER 5 A maintenance plan
5.1. Athens experience
5.2. Göteborg experience
5.3 Munich experience
This Good Practice Guide presents three different approaches of the management, conservation and
maintenance of outdoor bronze monuments in Europe. Athens, Göteborg and Munich are European
cities facing different problems and through this project they have tried to gather their experiences
which are presented in the following pages. This project would not have been possible without the
financial support of the European Commission and both the editor and the authors are grateful to the
European Commission for its essential contribution.
One might be careful while writing such a document, especially when just a few countries are
represented. The future readers of this document will find some advices, interesting comments or
experiences and some kind of methodology on how to manage, conserve and maintain our outdoor
bronze sculptures. But these texts do not intend to give a common European approach.
To write and publish such a document in less than one year has been a challenge. I would like to
thank then all the authors for their major contribution. Most of them did not only write their
chapters but gave constructive comments on the whole document. Nevertheless to respect their
particular approach, their name has been left under their different texts.
Christian DEGRIGNY
Zeta Antonopoulou: Archaeologist
Vasilike Argyropoulos: received a degree in chemical engineering from the University of Toronto in
1988. She was awarded a Ph.D. in archaeological sciences from the University of Bradford in 1992. She has
conducted research in conservation science since 1993 at the Historic Resource Conservation Branch (Parks
Canada), the Canadian Conservation Institute, and Arc'Antique, Nantes (France). Presently she is an
assistant professor in metals conservation at the Technological Educational Institution (T.E.I.) of Athens.
Address: T.E.I. Athens, Dept. of Conservation of Antiquities and Works of Art, Ag. Spyridona, 122 10
Athens, Greece.
Dimitrios Charalambous:
Christian Degrigny: received a degree in electrochemical and electrometallurgical engineering from the
National Polytechnical Institute of Grenoble in 1985. He was awarded a Ph.D. in Analytical Chemistry from
the University P. and M. Curie (Paris VI) in 1990. He has worked as a conservation scientist in different
conservation laboratories in France (EDF-Valectra, ART-Métal and Arc´Antique) and at the Australian War
Memorial. Since 1990 he has conducted research on corrosion problems and conservation treatments of
historical and archaeological aluminium, iron, copper, lead, tin and silver artefacts. Presently he is the Head
of the Conservation studies at EVTEK Institute of Art and Design, Vantaa, Finland.
Address: EVTEK Institute of Art and Design, Conservation Department, Lummetie 2, 01300 Vantaa,
Anke Doktor: received a degree in chemistry from the University of Duisburg in 1998 focused on
Instrumental Analysis. Since 1999 she has been working as a chemist at the Bavarian State Department of
Historical Monuments within different national and international projects dealing with bronze and copper
restoration and conservation.
Address: Bayerisches Landesamt für Denkmalpflege, Hofgraben 4, 80539 München, Germany.
Vasilike Leontari:
Martin Mach: works as a chemist at the Bavarian State Department of Historical Monuments since 1984.
He has coordinated national and international projects on metal restoration and is editor/author of books and
lectures about bronze restoration and conservation science. He has managed and supported some major
restorations of outdoor bronze monuments in Germany.
Address: Bayerisches Landesamt für Denkmalpflege, Hofgraben 4, 80539 München, Germany.
Kate Ryffé: is working at the Parks and Landscape Administration in Göteborg at the Department
of Arrangements.
Helena Strandberg: completed her education as an object conservator in 1986 in the Royal
Academy of Fine Arts, Copenhagen, Denmark, and worked as archaeological conservator for some
years. She also holds a BSc in Chemistry and in 1997 she received a PhD in Environmental Science
from the University of Göteborg, Sweden, on her cross-disciplinary research on outdoor bronze
sculpture conservation. Presently, she is working as a freelancing conservator and scientist, in this
project for the Parks and Landscape Administration in Göteborg.
Helen Svenstam: is MSc in Landscape Architecture. She is Head of the Department of (Parks care
and handling??) at the Parks and Landscape Administration in Göteborg which also are responsible
for the care of outdoor art.
1/ Presentation of the European project and the consortium (co-ordinator and partners).
2/ For the GPG:
Our objective with this GPG is not to concentrate only on the problem of the conservation of
outdoor bronze monuments, their construction and their conservation. These subjects have indeed
been studied thoroughly and a huge literature already exists (see the bibliography given at the end
of the GPG). We want in addition to give other approach of these monuments that might be useful
to a larger public. Social and historical aspects are then developed and are illustrated with case
studies. We emphasise too the importance of management and maintenance of these monuments
which have essential consequences on their protection and conservation in the long term.
The three cities considered here are facing different degradation and conservation problems of their
outdoor bronze monuments. One of the major achievement of this project has been to compare the
conservation approaches of each city and to discuss about the maintenance programmes. These
experiences will be added data to the study of outdoor bronze monuments all around Europe and
might be used to define a proper management and maintenance policy.
We hope with that GPG to produce a document that will be of some use to the professionals who
have to deal with the conservation of outdoor bronze monuments. Of course it can be improved and
we would be interested in your different comments…
The contributors
Urban planning for the protection of outdoor monuments
Managing our cultural heritage is a great responsibility. This responsibility goes along with the
obligation to preserve all monuments witnessing our civilization for the future generations. This
task requires knowledge, sensitivity, specialization, ability to co-operate and co-ordinate actions,
open mind and the existence of a powerful legislation providing for any intervention.
The role of the state
To begin with, as far as the role of the state is concerned, there is a major need to declare all
outdoor sculptures monuments. This assures their protection by a specific body and helps the public
to realize that they must respect them as if they were museum exhibits.
It is believed that all outdoor sculptures cannot be considered as monuments. At this point, an
important issue arises. It concerns the definition of a monument and the question whether it has to
be dissociated from the definition of a work of art. The philosophical aspect of this issue is yet
unresolved because opinions diverge about terminology. According to the definition that dominates
a monument is a witness of a civilization. So, outdoor sculptures can be undoubtedly considered as
monuments and not as objects just needing special care and protection.
The situation concerning the protection of outdoor monuments in Munich, Göteborg and Athens is
quite different. In the case of Athens, the majority of outdoor sculptures have not been declared as
monuments and consequently they are not protected by the law. The Traditional Buildings and
Monuments Division of the Municipality of Athens, responsible for this area for the last six years,
has always considered them as monuments representing art, Greek history and culture. They must
therefore be respected and all works have been carried out according to the rules of art and science.
However, their declaration as monuments is an issue which needs to be settled.
The role of the body responsible for the protection of monuments
The documentation of monuments is of great help for those managing our cultural heritage. This
enlightens all aspects concerning art, the history which justifies the existence of the monument, the
artist and the entire construction. Documentation does not only involve the collection of information
about the past but it also registers and files all present interventions which will be evaluated at a
later date.
All data gathered from the documentation are stored in a database. To be more exact, this database
contains historic data, data concerning the location and the description of the monument, the
biography of both the sculptor and the person depicted, relevant bibliography, reports on former
maintenance works and expertise on the condition of the monument. It is enriched by photographs
belonging to archives as well as photographs taken during the maintenance or restoration works.
It is obvious that this information is useful for an art and history researcher as well as for an expert.
It also facilitates the work of the body managing the sculptures because it enables them to monitor
their present condition, to study and programme all required interventions and mostly evaluate the
results of previous works. All this represents the objective of the maintenance plan that must be
included in the annual technical programme of the body.
It is also necessary to evaluate all monuments, a task easily carried out thanks to processing the
above data. The evaluation consists in defining the values that envelop a monument. In other words,
it is about a theoretical approach that could play a significant role in planning the maintenance or
restoration of the monument in order to promote these values. The values and the systems of values
(historic, aesthetic and artistic values, the landmark value, the value of symbolism etc) cannot be
here analysed because they constitute the objective of a philosophical approach in the history of
Monuments and citizens, a relationship to be restored
Promoting these values contributes to restore the message conveyed by the outdoor monuments, to
realize their meaning for the city and its citizens as well as their role in civilization. It also
contributes to identify the person depicted and the reason for his or her commemoration in order not
to insult their memory by vandalism or other shameful actions. Revealing the message of the
monument sensitizes citizens and society as a whole and determines their attitude towards the works
of art.
This objective can be achieved through an effective educational system and through information
campaigns. They are the result of both state and individual concern. However, it is disappointing
that few citizens recognize the existing outdoor monuments, that they pass them by without noticing
them and that they look at them without really paying attention to them. This can be explained by
Lack of information
Lack of signs
Abandonment of the sculpture
Inadequate cultural education
Great effort and real concern on the part of the state are needed in order to deal with all these
problems. Our suggestion concerns mostly the awakening of sensitivity and respect towards all
monuments witnessing our culture. Emphasis must be put on the most ductile and most sensible
social group: the children. The more they have an adequate approach to outdoor monuments, the
more we can hope for an appropriate future attitude. Educational institutions, teachers, parents,
bodies responsible for the protection of monuments, they must all motivate children, kindle their
imagination and talk to their soul. Educational programmes can take place at public places where
children can communicate with monuments and where many activities can be performed.
This perspective does not exclude adults from a sensitizing effort. This is possible by publishing a
maintenance study as well as all the issues arisen. It is also necessary to inform them about our
cultural wealth or launch a “protection campaign” which might cast publicity on this subject.
Maintenance plan
Following the historic documentation, the study of values and the definition of the elements causing
damage/corrosion, the objectives of maintenance works must be planned according to the principles
of science on matters of cultural heritage. This planning is an attempt to eliminate the damaging
elements and assure future protection. This might involve a direct or an indirect maintenance
project. The former demands the intervention on the monument and the latter the elimination of
damaging elements without necessarily intervening on the monument.
Direct maintenance has mainly to do with the monument´s surrounding place. It is quite easy to
determine the damaging elements linked with the surrounding place of a monument and then to
eliminate them. For instance, if the monument is easily accessible and has therefore been
vandalised, measures must be taken to make access more difficult. This goal can be achieved by
means of more natural and ecological solutions such as surrounding the monument with wide but
short bushes. In case a monument has suffered irreparable damage due to pollution or poor quality
of the material used, the only way to protect it is to remove and replace it by a copy. Pigeons can
also cause damage by polluting and subsequently corroding the surface of bronzes.
It is necessary to emphasise the importance of the surrounding place of a monument for the
monument itself because they are strictly associated. There is a major need to protect the
surrounding place in order to promote the value of the work of art and not to condemn it. It is also
worthwhile mentioning the wrong choice of places to host outdoor monuments. The only criterion
for selecting the location of a monument is the decoration of a place. For Athens, this attitude also
explains the fact that monuments are mostly found in the city centre while the districts are lacking
of these monuments.
The direct maintenance, the planning, the carrying out as well as the supervision and the evaluation
of the entire project require the co-operation of many experts such as conservators, chemical
engineers, art historians, architects, civil engineers, etc. This co-operation is hard to be achieved if
the parties involved lack of maturity. A mature and responsible attitude can be often fostered by the
body entrusted with the protection of monuments.
According to all declarations for the protection of our cultural heritage, maintenance works consist
in an irreversible intervention. It is therefore advisable to carry out works that do not have quick,
impressive or radical results because they might cause immediate or long-term damage to the
monument’s surface. There is a whole procedure to respect and follow: cleaning, fixing,
maintaining, restoring and protecting the monument. This procedure is planned by experts and it is
obvious that it does not apply to all cases. Planning and documenting the works carried out, the tests
done and their results are necessary for both the maintenance project and its evaluation.
Most theoretical issues involve complementing the figure or the symbol represented in order to
render it recognisable and deciding on the restoration of damage representing the history of the
sculpture such as holes by bullets that mark many sculptures in Athens. Decisions on such issues
must be jointly taken and require adequate knowledge of the subject and all the qualities mentioned
at the beginning.
Following the completion of maintenance works, one question remains: What is to be done in the
future? An option is to wait until the monument suffers a new damage to take further action.
It is however better to plan a programme monitoring the current condition of monuments (which is
not difficult thanks to the existing data base) in order to make a report on it on a regular basis and
then plan further action. The implementation of this project is of major importance for managing
properly the monuments. Last but not least, all parties involved in the protection of our cultural
heritage must act with a sense of responsibility and moral obligation to both past and future.
By Zetta Antonopoulou
The meaning of our outdoor bronze monuments to European citizens
1.1. Social and historical aspects
A sculpture represents a major expressive and creative way through which the feelings, the thoughts
and the concerns of an artist or a sponsor (like kings) are expressed
. At the same time people
understand the history by means of it. It consists one of the visual arts and it is therefore expressed
through the image, through what observers can see, through what the soul feels and perceives. The
result of an artist’s work, the sculpture, awakens various feelings to each one of us. Most observers
are satisfied by an aesthetic result belonging to the category of the “beautiful” and the “optimum”,
an admiration for giving shape to movements and sentiments, a result characterized as “three-
dimensional” and “spiritual”. The more the depiction is closer to reality, the more the public
understands it and feels awe. That’s presumably the reason for which the classical art principles
affected artistic expression regardless of the time period or the place.
1.1.a. Sculpture in public spaces
A sculpture becomes an art related to public when cities and generally organized societies are
formed. The sculptured work of art is no longer exclusively found in mansion gardens or royal
palaces; it is also placed at public places, it consists an element of the city, it belongs to the public.
It holds a monumental value, since it functions as an artistic creation commemorating events or
people. The work of art by itself or as a complement of a structure becomes a monument in
commemoration of a person, a historic or else event; it often expresses vanity or excessive egoism,
an idea or a political ideology. It undoubtedly shows the wish to familiarise future generations with
the history of their ancestors. It aims at preserving this witness to eternity. Many times it is simply a
reference, it plays a purely decorative role and the public simply admires it.
Creating and erecting a monument at a public place can be the result of an individual initiative, a
donation, or of a state concern, when the state wants to adorn the city and its buildings with
monumental or decorative sculptures. The monumental form or picture is and has been a part of the
methods for the official power to mark its influence and its connection to traditions. The public
spaces in cities accordingly have monuments placed as an indication that the power exists in the
public and daily life. Later in the 19th century the democratic ideas of the public art as an art
available to all people become significant. The art should belong to everybody and be the poetic
force in the society.
Outdoor monuments that are the subject of our study belong to the category of modern monuments.
They are associated with the urban development in Europe mostly in the 18th and the 19th centuries
based on the humanist values according to which the past must be commemorated and respected.
One of the German Kings (Ludwig I) e.g. had much influence on the patination of several sculptures.
1.1.b. Historical monuments
The monuments with historic value are usually found at places associated with the historic events
they represent (e.g. at the residence of the person depicted, in battlefields etc). They can also be
placed at a central point (a big square) sending out their message to all citizens. In Europe these
monuments mostly depict princes, kings, pontiffs, eminent figures. In the late 18th century and
mainly in the 19th century they at last depict men of letters and artists. Great historic deeds are
usually commemorated by architectural monuments such as columns and arches, which is not the
case for the 19th century Greece. In the 20th century, following the two World Wars, the need to
commemorate rises again. However, the types and the subjects of historic monuments have reached
saturation point.
The increase in the number of monuments and the exhaustion of subjects along with the historic
developments resulted in a range of new subjects inspired by the lower and humbler classes of
society. It is doubtful though that there is an intention to glorify humble people. The depiction of
everyday life is associated with more democratic societies. In this case, however, everyday life is
not awarded a historic or honorary value but an artistic and a rather decorative one.
1.1.c. Decorative monuments
The monuments of decorative character are placed in parks, big gardens, squares, avenues. They are
considered as autonomous, that is to be they are not the result of a commission limiting partly the
inspiration of the artist and they do not have a historic meaning. These monuments serve an
embellishment purpose and they are often combined with water (fountains and lakes). Adorning
gardens is an idea developed in the second half of the 16th century in Europe (Italy, France -
Versailles). This idea is materialized in the streets and the parks of the cities when open spaces
justifying or requiring a monument are designed. This tendency reaches its peak during the Rococo
and the Baroque periods.
If one wants to classify the outdoor monuments, the following categories exist: statues, equestrian
statues, busts, heroic monuments, free compositions, groups. As far as the material used is
concerned, the relevant categories include marble, stone, bronze, metal, glass etc.
Outdoor monuments have both a historic and an artistic character. The latter automatically places
them among the works of art. All works of art convey a message to us: it is the simple identification
of the figure or the event represented and commemorated. There is a need to keep the history
engraved in our memory, which is the initial objective of the creation of the sculpture.
1.1.d. The meaning of outdoor monuments
In addition, a considerable number of important information on civilization is gathered by observing
and studying sculptured monuments. This information involves the style, the medium and the
process of creation. This is an important material for studying the History of Art, the influences
interchanged among nations. It is really impressive the fact that art has no limits, that it assimilates
and expresses the qualities and characteristics of each culture. Significant information is also
collected about the techniques used for the creation of a sculpture, the marble-works, the foundries
as well as about the technology of media by studying the corrosion and the damage suffered due to
the exposure to the environment.
In conclusion, monuments play a major role in the history of the city. In a matter of speaking, they
represent the history of a city since the citizens identify in them personalities, heroes, benefactors,
mythological and historical scenes, deeds of heroism. One can collect useful information by
studying their location in the town planning network, or touching information by studying details
such as the marks of bullets on many sculptures in Athens.
The outdoor monument represents for the majority of us an expression of art and civilization. By
observing the monuments of our city, a part of our everyday life, their grandeur will move us.
By Zetta Antonopoulou
1.2.The Bronze monuments in Athens
1.2.a. Historical basis
In 1830, Greece is recognized as an independent state.
This period signals the end of a long effort
aiming at liberating the country from the Turkish rule, finding its national identity as well as a place
among the other independent states of the West.A few years later in September of 1834 Athens
becomes the seat of the Greek monarchy and the capital of the independent Greek state.
Frederic Otto, second-born son of the Kind of Bavaria, Ludwig I , has been appointed as King of
Greece3. Otto’s arrival, and his staff, consisted of Bavarian scientists, is followed by a period
dedicated to the concern for the antiquities and the new artistic creation, thus achieving the
ideological support of the new state.
At that moment, the population of Athens is about 8000 people and a project regarding the building
of the capital is implemented. This project is based on the town planning network designed by
Stamatis Kleanthis (architect, Berlin’s Academy graduate) and his colleague Edouard Schaoumbert
focusing on the royal palace of king Otto.
In Athens flourishes the movement of neo-classicism.4 The newly built city mirrored the urban
architecture: public buildings of rare beauty and aesthetics illustrate this tendency. Moreover, these
buildings aim at endowing the city with a monumental character worthy of a glorious past, of Greek
antiquity. At the same time, there is a need for the city to resemble to other European cities.
1.2.b. The appearance of sculpture
As a consequence of the above, all kinds of arts bloomed including sculpture, an art promoting the
image of our country in exhibitions abroad and creating important and outstanding works of art.
Greece’s independency was recognized with the signing of the London’s protocol, in February 1830.
2 Nafplion had already been nominated as a temporary capital of Greece. Among the cities that have claimed for capital
(Athens, Corinth, Nafplio, Argos, Tripoli, Syros, Megara) Athens had a fair chance of winning due to its ancient glory.
An important factor that had also contributed to the selection of the city was that Athens had the favour of the Bavarian
King, Ludwig, Otto’s father.
3 By protocol in May 1832 in London.
4 The classicism, as a result of the movement of philhellenism and the tours in the Greek province, has already been
created, disseminated and prevailed throughout Europe and especially in Bavaria. After Otto and his staff , consisted of
Bavarian, was installed in Athens, German classicism was introduced and assimilated as revealed by the Athenian
public buildings designed by north European architects. As a result of this assimilation, we had the processing, the
adaptation to the Greek reality and, finally the differentiation from the west European prototypes. The neoclassicism in
Athens was characterized by the simplicity, the vividness and the fitting to the simple urban architecture.
Art is no longer exclusively present at private places (e.g. the residence of a wealthy bourgeois who
could afford the commission of a statue) but also at public places : squares, parks and avenues are
adorned with statues of various forms, sizes and subjects. Their creation results from state or
individual initiative and is part of a project to decorate the city. It is of great interest to observe
statues commemorating a person or an event that are not playing a simple decorative role. The first
sculptures meet this wish. The glorious past of the heroes of the Independence War, philhellenes or
benefactors constitute some of the favourite subjects. They also meet the need of the nation to show
their gratitude, to be inspired while continuing to struggle and hope. The statues of ancient gods are
lasting reminders of the grandeur of classical Athens and awaken in the soul of modern Greeks a
feeling of pride and superiority. As it is obvious, the power of sculpture is beyond a simple artistic
expression; it is a national need for memory and honour, need of national evolution.
At this point, we could not fail to mention a place where some of the most important outdoor
sculptures are on display: the First Cemetery of Athens (Fig. 1.1). This place helps us to observe the
evolution of art, its variety and the creations of some of the greatest artists. It also gives us the
opportunity to admire remarkable works of art.
Fig. 1.1.: The First Cemetery in Athens (general aspect). Credit Municipality of Athens, Department of Traditional
Buildings and Monuments.
The sculptures in Athens are mainly made of marble. The clarity and the transparency of marble has
often been associated with the Greek light. Marble was particularly popular in antiquity and found
in abundance in the hills surrounding the city. It was easily quarried and processed by craftsmen.
Most of these craftsmen who settled and worked in the capital for many years, were from the island
of Tinos which had the longest tradition in plastic arts and marble-sculpture.
Bronze as a medium used by sculptors appeared many years later. The first sculpture was erected in
Athens in 1834 (the monument of the Holy Company of 1821)
while the first bronze monument
was the statue of general Theodoros Kolokotronis that was cast in 1900 and erected in the capital in
1904. The absence of bronze sculptures is due rather to practical reasons: the lack of foundries for
large constructions. A great quantity of bronze was needed for the construction of the Kolokotronis
statue in Nafplion (about 5 tons) which was found by melting gun fragments dating from the
Turkish invasion. The selection of these bronze pieces was made by Trikoupis, the then Minister of
All the early bronze sculptures of Athens were made abroad by Greek sculptors or foreigners.
Lazaros Sohos for instance who worked the Kolokotronis statue lived in Paris from 1881 to 1901
and was particularly influenced by Marie-Jean-Antonin Mercié, one of the most eminent academic
sculptors of the time. The foundry where the statue was cast, was one of the best in Paris.
According to sources the majority of the most important statues of Paris were made there. It was
the Thiebaut Frères foundry housed at 33, Quessant street. Its name inscribed on the statue (actually
their name is associated with the name of their successor L. Gasne) and embossed on its base
confirms this information.
The name of foundries on many bronze sculptures gives important information on the history of art
and the history of a civilization which have both a local and an international character.In more
recent times, foundries operated in Greece but it appears that their operation will eventually stop.
The most important foundry where most bronze sculptures of the 20th century were made is the the
Army Foundry.
Γιαννουδάκη Τ. ,Τα υπαίθρια γλυπτά του Δήμου Αθηναίων 1832-1922,Μεταπτυχιακή εργασία,ΑΠΘ, 1994
Out of 220 sculptured monuments in Athens, the bronze ones (63 registered until now) represent a
percentage of about 30%. Most of them have been made during the last years. Nowadays, artists
prefer metal possibly because it is in abundance and more resistant than marble to pollution and
environmental conditions.
Art passed through many phases following the major historic moments of the nation before ending
up in a polymorphism, in the freedom and the variety of the media used.The sculptures cast in
bronze are mostly equestrian statues [T. Kolokotronis, King Constantine, (Fig. 1.2) Georgios
Karaiskakis], statues [K. Palaiologos, (Fig. 1.3) Archbishop Damaskinos, O. Elytis etc], free
compositions inspired by the Greek mythology- [Theseus saving Hippodameian (Fig. 1.4)],
modern creations [such as the monuments commemorating respectively the Air Force soldiers fell
on the field of honour and the National Reconciliation(fig. 1.5)], lamp-posts (adorned with
cupids)(Fig. 1.6), busts [Christophoros Nezer, Dominikos Theotokopoulos (Fig. 1.7), Athanasios
Lefkaditis etc].
Fig. 1.2.: Equestrian statue of King Constantine at Pedion tou Areos.It was made in Italy , by the architect Taetriani
and the sculptor Parisi, and was erected in 1938. Credit Municipality of Athens, Department of Traditional Buildings
and Monuments.
Fig. 1.3.: Statue of Constantine Paleologos IA’ , at Mitropoleos square.It was made by Sp. Goggakis at 1989. Credit
Municipality of Athens, Department of Traditional Buildings and Monuments.
Fig. 1.4.: Theseus saving Hippodameian at Victoria’s square, by the German sculptor Joh. Pfuhl,in Berlin at
1906,donated at the Municipality of Athens at 1927. It was erected at Syntagma square at first. At 1938 it was
transferred at its present location. Credit Municipality of Athens, Department of Traditional Buildings and Monuments.
Fig. 1.5.: Lamp-post in Kypseli, made by A.Durenne in Paris,end of 19th century-beginning of the 20th. Credit
Municipality of Athens, Department of Traditional Buildings and Monuments.
Fig. 1.6.: Monument of the National Reconciliation at Klafthmonos square,made by Doropoulos Vassilis at 1988.
Credit Municipality of Athens, Department of Traditional Buildings and Monuments.
Fig. 1.7.: Bust of Dominikos Theotokopoulos at Akadimias street,center of Athens,made by kostas Valsamis in Paris. It
was erected at 1990. Credit Municipality of Athens, Department of Traditional Buildings and Monuments.
It is easy to understand that outdoor bronze sculptures in Athens, even if fewer than the marble
ones, give us a wide range of information on the artistic tradition,their construction, the history of
the city while representing monumental creations of incomparable art and beauty.
By Zetta Antonopoulou
1.3. Bronze sculptures in Göteborg – kings and fighters, water and shipping - donations and
the art for everybody
Göteborg - a city with the population of 500.000 habitants is situated at the West coast of Sweden.
The proximity to the sea and the harbour are some of the characteristic features of the city. Today, it
has as many as 600 artworks. Monuments, sculptures, busts and fountains embellish streets, squares
and parks both in the city and in the suburbs. Among the outdoor artworks, bronze is the dominant
material category presenting 200 of the sculptures in the city. Other material of sculptures during
the 19th century is e.g. granite, iron, zinc and in few cases marble. Since the second part of the 20th
century, concrete, enamel, wood, glass, and plastic have also became common materials for outdoor
From a historical perspective, Göteborg, founded in 1623, has statues dating back to the middle of
the 19th century, the oldest statue in bronze being the monument of the king Gustav II Adolf from
1854 (Fig. 1.8). Only a dozen of the bronze sculptures were inaugurated before the 1920’s.
Accordingly, most artworks in Göteborg are modern and have been erected after the 1950’s when
the art was brought out to the people on the streets in Sweden.
Figure 1.8.: Gustav II Adolf standing highly erected pointing at the ground of Göteborg that he founded in 1623. This is
the first bronze monument in the city and was cast in 1854. The monument was made by the sculptor Bengt Erland
Fogelberg (1786-1854).
1.3.a. Water, shipping and trade
Something that people often remembers after visiting big cities is the sculptures. They are on post
cards and as pictures in the visitors’ mind. Those who have visited Göteborg probably will
remember the large bronze sculpture Poseidon surrounded by sparkling water cascades in a fountain
located in the middle of the place Götaplatsen (Fig. 1.9). Both the place and the artwork are
monumental. In the background the immense façade of the Museum of Art is built in the austere
style of the 1920’s. Poseidon is created by Carl Milles (1875-1955), a Swedish sculptor with
worldwide fame. Characteristic for Milles is the classical motifs often taken from the mythology.
The powerful Poseidon, 7 m high, has become a profile for the city of Göteborg situated at the
Figure 1.9.: The Poseidon fountain by Carl Milles (1875-1955) was erected 1921-31.Credit?
The first sculpture of a woman in public space surmounting a fountain in central Göteborg had the
French name “La Semeuse” (Fig. 1.10). The artwork is from 1883 and was inaugurated on the day
of Johanna after which the sculpture in popular speech was named “Johanna”.
Figure 1.10.: “La Semeuse” from 1883 by Per Hasselberg is the first sculpture of a woman in the city.Credit?
Particularly the water, shipping and trade are the theme in many of the public decorations in
Göteborg. Here are the Tritons, nymphs, ships, waves, fishes etc. Also the seaman’s wife waiting at
the shore a sculpture placed on a campanile highly erected above the sea in Göteborg harbour.
One group of sculptures placed in the square Järntorget also turn the minds to water and the trade
ways linking countries together (Fig. 1.11). The fountain Järntorgsbrunnen was created as a
memory of iron-cargo shipped to countries far away. The five women placed on the rim of the
fountain symbolize the five parts of the world. Another monument recalling the wide world, in this
case America is the Delaware monument on the pier in the harbour.
Figure 1.11.: In the fountain “Järntorgsbrunnen” (inaugurated 1927) by Tore Strindberg the five women are
symbolizing the five parts of the world where the iron-cargo were shipped to from Göteborg harbour.Credit?
Sculptures of younger date, from 1990’s, are the two lions lying on granite bases on both sides of
the Lion stairs in central town, guarding the western sea entrance to the city. Another modern figure
in the city centre is “The Neck is playing”. The evil spirit of the water is both beautiful and
dangerous and with the music of his violin he is seducing and drowning people in the water.
1.3.b. The men and female characters
In Göteborg, as in most places in the world, art in public space has been created to embellish cities
and celebrate the memory of persons or events. It also gives patrons of the arts a possibility to leave
behind something of long-lasting value. So did also Charles Felix Lindberg, a tradesman who at the
turn of the century donated large amounts to the decoration and embellishment of the city of
Göteborg. His money still today is used for the decoration of the public space. Many of the
sculptures that have been created by these donations are in the city centre. Several of the older ones,
from the end of the 19th century and the first decades of the 20th century have the characters of
national romanticism. They are figurative and often represent famous men of the country. Others
are monumental, figuring kings and mythical shapes. Some sculptures are also women, in most
cases featuring nature as “The spring”, “The haze”, “Summer”, “Flora” and others (See Fig. 4 ? of
the Haze).
1.3.c. Kings and fighters
One expression of the political power is the statue from 1854 figuring the Swedish king Gustav II
Adolf standing highly erected pointing at the ground of the city he founded 200 years earlier (Fig. 1.
8). The square where he is placed is named after the king and is Göteborg’s official centre. An
additional statue mediating the power is “Karl IX”, a Swedish king riding on his horse. Nobody
could imagine at the grand inauguration in 1904 that the artwork should later be named “The copper
mare” and become one of the popular meeting places in the city. “The knife-wrestlers” is another
historical sculpture that have given name on the park where it is placed (See fig 4.??). The motif is
Old Norse depicting two young fighters strapped together with a belt, fighting a violent life-and-
death struggle.
1.3.d. Unobtrusive and in a class by itself
If you ask to the citizens of Göteborg what sculpture they like most, many would answer ”Karin
Boye”, a figure of one of our well-known poets in simple summer-dress viewing the largest
commercial street in Göteborg (Fig. 1.12). The figure is unobtrusive, loved and also cared for. Often
fresh flowers are slipped into her small hands of bronze. “Karin Boye”, inaugurated in the middle of
the 1980’s was the first named statue of a well-known woman placed in Göteborg.
Figure 1.12.: The bronze sculpture of “Karin Boye”, a well-known Swedish poet, is loved and cared for (by Peter Linde
1.3.e. Forming the place for everybody
Many sculptures created in the 1960’s, 70’s and 80’s are in the local centres of the suburbs.
Decisive for these art projects were the expansive house-building and the one-percentage-rule
demanding that one percentage of the costs for new buildings should be invested in the public
embellishment. One characteristic feature for the late public art is that it is an integrated part of the
environment. Another is the democratic idea of public art as an art available to all people. The art
should belong to everybody and be the poetic force in society.
One good example where the sculpture forms the place is the “Reclining figure” by Henry Moore,
an abstract piece of art from the 1960’s that enriches the large central park Slottskogen (Fig. 1.13).
Sculptures in Göteborg today mainly associate to modern ones. Several artworks have been shown
in Park exhibitions with the aim to give guidance in looking at art and to reach a wider audience
which also have been successful.
Figure 1.13.: “Reclining figure” by Henry Moore (cast 1961) in the large central park “Slottskogen”.
By Kate Ryffé and Helena Strandberg
1.4. The importance of outdoor bronze monuments in Munich
There is a considerable number of Outdoor bronze monuments in Munich. At least ten of them can
be dated back to the time before 1800. Among this oldest group are also complex monuments, such
as the Wittelsbacherbrunnen consisting of many individual figures and ornamental parts and the
famous Mariensäule (Marian column) with a gilded bronze Madonna on top of the column as well
as four groups of Putti fighting evil forces.
At least thirty life-sized or more than life-sized outdoor monuments date back to the 19th century,
among them we find such prominent objects as the Bavaria monument and a bronze lions’ quadriga
5 m in height (Fig. 1.14). The most famous bronze monument in Munich is the so-called Bavaria, a
personification of the Bavarian state (Fig. 1.15).
Figure 1.14.: Close-up of 5m high lions´quadriga on top of the Siegestor, by Johann Halbig, unveiled in 1852. Picture
before restoration by the Municipality of Munich in 1996-97. Credit Bavarian State Department of Historical
Figure 1.15.: The Bavaria Monument, by Ludwig Schwanthaler (1850) in front of the Hall of Fame, height of the bronze
figure 18 meters. Visitors can walk up inside to the head and have a look around through three small windows on top of
the head. Credit Bavarian State Department of Historical Monuments.
This gigantic bronze sculpture was designed by Leo von Klenze as the architect and Ludwig
Schwanthaler as the artist. It was unveiled in 1850 by Ferdinand von Miller who had established the
Royal Bavarian Bronze Foundry in 1824. For the largest piece, the upper part of the body, about 25
metric tons of bronze had to be melted. The overall weight of the bronze parts of the Bavaria is
about 70 tons. In comparison the typical weight of a 3 m bronze statue is usually in the range of
about only 2 tons. Visitors can enter the Bavaria through a bronze door at the back of the stone base
and climb up to the head via a flight of winding stairs. There are two “bronze cushion“ seats inside
the head where visitors can sit down and have a look at the Theresienwiese area (the place of the
annual Oktoberfest). Even today the Bavaria is among the biggest bronze monuments worldwide
and one of the very few that can be studied from the inside.
Around the middle of the 19th century a new generation of monuments was devoted to famous
citizens like the founder of the Munich optical industry Fraunhofer (Fig. 1.16), to Schelling the
philosopher and to Count Rumford (Fig. 1.17), an ingenious multi-talented man who worked on
thermodynamics as well as on city park design and the improvement of the nutrition of the poor.
Figure 1.16.: Fraunhofer Monument, by Johan Halbig, unveiled in 1868, after restoration in 1998. The restoration was
funded by the Rotary Club München. Credit Sachers.
Figure. 1.17.: Count Rumford Monument, by Kaspar Zumbusch, unveiled in 1867, after restoration in 1998. The
restoration was funded by the Rotary Club München. Credit Sachers.
Though the monuments are an important part of the townscape many citizens are not really aware of
their presence and significance. Of course tourists take typical photographic snapshots in front of
the monuments e.g. with the family standing on the base of the monument for King Max Joseph I
(Fig. 1.18) in front of the opera, with the hands on the bronze lions’ legs. There is also an old saying
that rubbing the nose of the small lions’ heads in front of the Residence will provide a certain
wealth for the person who does it.
Figure 1.18.: Monument for King Max I. Joseph, by Christian Daniel Rauch, unveiled in 1835, before restoration by the
Municipality of Munich (1988). Credit Bavarian State Department of Historical Monuments.
Only great changes like restorations or the absence of a monument will be noticed by newspapers
and people passing by, thus giving back some of the lost attention to the monument. Recent and
present restorations, e.g. those of the Mariensäule and of the Bavaria have brought back a great part
of the public interest. It was a big and positive surprise that a 45 minutes television documentary on
the history of the Bavaria monument was able to compete with soap operas on other TV channels.
By Anke Doktor and Martin Mach
The construction of an outdoor bronze sculpture
Before dealing with degradation and conservation aspects of bronze monuments, it is essential to
know how these monuments were constructed. It is the aim of this chapter to give some general
ideas on the subject and more particularly on the bronze sculpture which is the most complex part.
Since ancient times people have been forming metals and creating bronze sculptures. The processes
for bronze casting have improved throughout the centuries in Europe but even today the skills of
ancient Chinese foundry men have been unsurpassed. In most countries the so-called lost-wax
process was the first attempt to solve complex casting tasks. In the 19th century the different
variants of the sand-casting process became familiar, in particular for very large monuments. But
they did not completely replace the lost-wax process. A further process, by which metal sculptures
were created, was established in the middle of the 19th century: it was called electrotyping (a
procedure which forms a metal layer by means of galvanic deposition). Typical electrotype
sculptures consist of a layer of pure copper that has a similar outer appearance as bronze. As they
are sometimes misinterpreted as bronze sculptures, they should be mentioned here as an aside.
Though many modern variants of bronze casting were established in the technical field, bronze
sculptures have been cast through centuries either by means of the classical lost-wax process or by
means of the sand forming process.
2.1. The lost-wax process
Figure 2.1. shows this most familiar process for artistic casting. The lost-wax process is based on a
negative form of the original sculpture. The form is made out of plaster which is covered on the
inside by a wax layer of approximately 0.5-1 cm thickness. In a second step the space inside the
plaster form behind the wax layer is totally filled with clay mixture on an iron armature to support
the structure. The resulting wax layer is a very thin layer between the plaster negative and the
clay/brick core. Afterwards the plaster negative will be removed and fine details can be added to the
wax surface. The entrance tubes for the molten bronze are formed out of wax and joined to the wax
surface. After that the whole casting form is covered by several layers of complex clay-based
mixtures. Core pins help to fix the distance between the casting core and the outer form. Heat is
applied to melt the wax and create a hollow space for the metal. When all the wax has flown out of
the form, the inner and outer casting form will be heated before the molten metal is cast in. This
burning process will stabilise the casting form chemically and mechanically so that it will not be
cracked during the casting process. At last the molten metal is poured through the tubes into the
hollow space between the inner and outer form.
The lost-wax process is expensive, laborious and risky. A minor defect in the construction of the
mould might endanger the whole procedure.
Figure 2.1.: The lost-wax process. Yellow: Heated wax flowing out of the form. Red: Hollow space left by the lost wax
for the bronze. Blue: Trapped air within the form must escape by means of special vents. From Boffrand, Paris 1743.
2.2. The sand-casting process
In the 19th century most bronze monuments were cast by means of the sand forming process. The
forming material for the outer form and the core consists of sand. Before the casting the clay form
has to be heated until there is no more water in it. If there is only a minute amount of water the
molten metal flowing into the form would create steam that might burst the form within seconds.
Normal sand without any binder would disintegrate during the drying into single grains, but a
comparatively small amount of clay mineral in the sand will help to create a fire-proof mould.
As stated in the discussion of the lost-wax process, also in this case the aim is to create a hollow
space between the outer form and the casting core where the molten bronze will be filled in. The
process begins with an artist’s model, usually in clay. From the original, piece moulds are taken to
make a plaster replica (a positive). After the plaster replica has dried and been shellacked, it is half-
buried in a bed of sand held in a rigid metal frame, usually cast iron or wrought iron (Fig. 2.2.a).
The surface of the plaster is dusted with talc as a separator or release agent, and the sand is packed
firmly in place, a process called ramming. At the end the exposed top half of the sculpture will be
covered by a series of small, carefully moulded sand pieces (Fig. 2.2.b). The form pieces are fixed
by core pins in the outer layer of sand and the whole negative form is then dusted with talc or
carbon dust for an easier removing from the cast bronze later on. The pieces of sand are held in
place by a coarser outer bed of sand, supported in a second metal frame and again rammed to
stabilise the material (Fig. 2.2.c). This same process has to be carried out for the other side of the
plaster replica (Fig. 2.2.d and 2.2.e). After that it is very important to extract the plaster replica
without disturbing the very fine sand mould pieces (Fig. 2.2.f).
The void within the two halves of the mould is filled with a core. The core is constructed around an
armature made of iron pipe, rod or wire (Fig. 2.2.g and 2.2.h). Some rods project out and serve to
steady the core in the mould during casting. The core material usually contains plaster, sand
furthermore wax rods or organic material. The basic idea behind this is to make the core material as
porous as possible because it will expand and contract during the heating and cooling of the bronze
casting process. Now the inner form is almost completed but it still fills up the entire cavity
formerly occupied by the replica. So it has to be scraped back to generate a hollow space for the
bronze (Fig. 2.2.i). Now the surfaces of the halves of the mould are pierced in a number of places to
provide channels that serve various purposes (Fig. 2.2.j). Some channels, called gates, allow hot
metal to enter the empty space; others, called vents, permit gas to escape during the casting process.
The metal is melted in a crucible and poured into the mould through funnels.
During the casting, it is possible that the sand pieces shift a bit or get small cracks. This causes
characteristic seams in the sculpture that have later to be worked over.
A very good indication that a bronze monument is made by the lost-wax process is the great number
of core pins keeping the distance between the core and the outer form. Core-pins are always absent
in the sand forming process because they do not provide stability in the sand.
Figure 2.2.: The sand-casting process and working steps. From Lüer, Leipzig ~1902.
2.3. What is bronze?
Pure copper is not as fusible as bronze because it spatters during the casting and sets under
blistering. Therefore there are only very few monuments of cast copper worldwide. Copper alloys
with tin (Sn) and zinc (Zn) are better to cast than pure copper. The composition of art foundry
bronzes changed over time. Whereas the oldest Egyptian bronze sculptures were made out of a
mixture of copper and lead the Greek and Roman bronze sculptures contained less lead but more tin
and zinc. The German bronze sculptures of the Middle Ages were predominantly copper alloyed
with tin and only a very small amount of lead or zinc. But there are a lot of brass monuments in the
Nuremberg area.
19th century chemists considered a pure tin bronze as the very best choice in order to achieve a nice
natural patina. Foundry men liked to have more freedom and had individual habits. Casting
procedure were always optimised for certain alloys. This practise has roots in the history of each
foundry where an alloy which gives good results will never be used in another. A good illustration
of this empirical approach is the consideration by many foundry men in Germany that the alloy used
by the famous J.B. Keller in France for his famous equestrian monuments was the best suited for
big bronze monuments. It had even a proper name in Germany (“Keller-Bronze”), but chemists did
not agree with this.
In the beginning 20th century it was considered that the best bronze contains 90-93% Cu and 7-10%
Sn. The 93% Cu/7% Sn-bronze was used especially for the bronze sculptures in Germany of the
modern age For smaller monuments and ornaments mixtures of 88-92% Cu, 8-6% Zn and 4-2% Sn
were used.
The use of various copper alloys lead to different characteristics for the bronze sculptures. The
addition of Sn increases the hardness of the metal and the quality of polishing of the material, while
Zn improves the pourability. Lead increases the image sharpness. Depending on the history or
origin, the bronze contains other traces like nickel (Ni), silver (Ag), antimony (Sb), arsenic (As) or
iron (Fe), but as metal traces they do not influence the metallurgical properties of the bronze metal.
The famous Chinese mirror alloys contain between 20 and 27% tin and up to 6% lead so that they
have a silvery-white colour and resistance against colour changing. However this type of alloy is
brittle and difficult to engrave.
Copper and tin can easily be mixed by heating to high temperatures in the mass ratio that is typical
for bronze. During the cooling of the copper alloys after the casting the copper-tin mixture hardens
first in mixed crystals. Lead is completely insoluble in these mixed crystals and stays liquid for a
longer time because of its lower melting point. So lead hardens at last between the copper-tin
crystals and fills even the smallest unevenness between metal and form. So it is obvious that a
higher content of lead within the copper alloy leads to an increasing image sharpness.
Table 2.1 shows some types of copper alloys and their different compositions. There are two
fundamentally different types of bronzes called red brass (Rg) and tin bronze. Tin bronzes only
contain copper and tin whereas the red brass alloys contain also small amounts of zinc and lead.
Type of copper alloy
Cu [weight %]
Sn [weight %]
Zn [weight %]
Pb [weight %]
Rg A
G-CuSn4ZnPb (Rg 4)
G-CuSn5ZnPb (Rg 5)
G-CuSn7ZnPb (Rg 7)
G-CuSn8Zn (Rg 8)
G-CuSn9Zn (Rg 9)
G-CuSn10Zn (Rg 10)
Table 2.1.: Types of copper alloys used in casting and their different compositions. From Deutsche Norm, DIN 1705,
Kupfer-Zinn-und Kupfer-Zinn-Zink-Gu
legierungen (Gu
-Zinnbronze und Rotgu
), Berlin November 1981.
2.4 What is a patina?
As the discussion of this question fills books it is not possible to describe the term "patina"
appropriately within two pages. So discussion about patina is controversial and wide ranging, but
most conservators are in agreement that a patina on a bronze sculpture should be such as that the
bronze still bears its peculiar metallic character. Nevertheless there is no clear distinction between
the terms "patina" and "corrosion layer". From a corrosion scientist’s point of view both terms
describe similar chemical situations. E.g. a patina and a corrosion layer both might have
incorporated deposited material from outside like fat from touching or traces of dirt. But as a rule
the concept "patina" includes an aesthetic appreciation whereas the term "corrosion layer" does not.
A major benefit of a patina in the positive sense of the word is that it protects the metal against
destruction by environmental pollution and furthermore might be of a positive aesthetic value.
Figure 2.3 shows a cross-section of a sample from an outdoor bronze sculpture. This is an example
of a naturally grown patina that is no more protective.
Figure 2.3.: Typical cross-section of an outdoor bronze sculpture (width: 0.6 mm). The assumed original surface has
been destroyed to a great extent in the green areas.
There are two types of patina, natural and artificial. "Natural" or "artificial" refers to the causes of
the patina formation, so a natural patina means that it has been formed by environmental influence
only. The terms do not tell us whether the respective layer is stable or not. Some people prefer to
distinguish "outdoor patina" and "indoor patina", with outdoor patina being dominated by green
basic copper sulphates and indoor patina as a brown cuprite (copper-I-oxide) patina. An artificial
patina is maintained by applying chemicals or paint onto the surface of the bronze sculpture to
provide an "antique" finish or for various styles of coloration. Many modern sculptures are
artificially patinated.
To focus on the characteristics of patina on bronzes, it is necessary to have a look on the
vocabulary. There are four basic attributes of a patina on bronze sculpture; these are typically paired
as "natural" and "artificial" and as "stable" and "active". The terms "stable" and "active" refer to the
condition and reactivity of the patina and distinguish between two kinds of bronze corrosion. The
so-called "noble patina" consists of corrosion products that are at the same time attractive and
chemically stable. This type of patina is for example often found on excavated Etruscan and
Chinese mirrors. A stable patina is hard to find outdoors in these days because it is formed over a
long time period with little pollution. As a consequence there is only a slow corrosion and time
enough to form a stable corrosion layer. A noble patina on outdoor bronze sculptures can be defined
as a green or brown, shiny, peculiarly attractive, translucent surface which leaves no doubt that the
metal lies beneath. The translucent surface does not result from treatment but is simply caused by
gentle patina formation. It owes its beauty not only to a green colour. As a rule warm, red-brown
tones are displayed as well. The original contours of the bronze with all its finishing details must be
visible and the patina should have an enamel-like surface.
A chemically and mechanically stable patina normally has a glossy, translucent surface and a dense
smooth layer of brownish cuprite (copper-(I)-oxide) close to the metal surface. The smoothness and
gloss of the surface can be enhanced by the occasional touching of passers-by. The active or
virulent patina consists of those corrosion products that actively corrode the metal surface. It is
mostly of modern origin, namely caused by industrial pollution (presence of sulphates see below)
and can be found on the surface of urban outdoor bronze sculptures but also on very old
archaeological bronzes (presence of chlorides).
In modern times sulphur dioxide air pollution has formed light-green patinas consisting of basic
copper sulphates. This kind of look has become familiar and is sometimes described as a typical
natural patina. This modern type of patina might be protective in some cases for the metal but is not
very stable mechanically and chemically. However it might have a cultural value and carry marks
from tools and other information. Sometimes it is considered to have an aesthetic value but of
course the judgement may vary from object to object and among people and cultures.
A scientific clue to the understanding of the character of a natural outdoor patina lies in the
properties of the base material. The patina will develop in a positive manner when the alloy is
homogeneous, fine-grained, dense and not too porous. The surface has to be so smooth that
oxidation occurs very slowly.
Finally it has to be pointed out that there are always exceptions and special cases. This short
overview is intended as a quick information only and cannot replace the study of actual monuments
and further literature as mentioned above.
By Anke Doktor and Martin Mach
Deterioration of outdoor bronze monuments
3.1. General principles on the corrosion of copper based alloys
Metals have the tendency to corrode. Obtained from stable minerals which had to be melted or
transformed, they tend with time to come back to their original state.
This statement is well understood by everyone and conservators looking after metal objects know
very well that if such an object is left unprotected in the harsh atmospheric or other environment, its
appearance will gradually change and its surface will become covered with streaks, run offs, and
disfiguring corrosion layers.
Corrosion processes are taking place at the atomic level and involve not only the metal itself but the
environment (mostly humidity, oxygen O2 and other gas present in the atmosphere). Exchange of
electrons are involved in electrochemical processes and conduct on the metal surface (M) to the
dissolution of positive charged metal particles (cations M+) and from the environment to the
formation of negative charged particles (anions OH-). Both particles react to form a more or less
protective film (M(OH)n) on the metal surface (Fig. 3.1).
Figure 3.1.: Representation of electrochemical reactions taking place at the metal surface.
Heterogeneities and defaults present at the metal surface, particularly in the case of alloys (pores,
boundaries between grains of different composition, inclusions combining the different elements…)
are preferential site for corrosion processes. According to the metal microstructure they will
develop from pitting corrosion to general corrosion (on the whole surface or inside the metal).
Water tends to favour corrosion processes but oxidation also occurs in dry atmospheres and may
even conduct to the formation of a very protective oxide film.
Usually atmospheres are classified as rural, urban (SO2 deposition rate 10-80mg SO2 per m2/day),
industrial (SO2 deposition rate> 200mg per m2/day) and marine (between 5 to 500mg NaCl per
m2/day and can be as high as 1500mg).
Copper and bronze have always been regarded as corrosion resistant materials in outdoor
environments in comparison to iron alloys but the metal surface may be heavily damaged (etched).
Corrosion rates have been recorded in field exposures of copper and bronze coupons in different
environments, The general rate is higher on copper than bronze and is slightly higher on unsheltered
samples than on sheltered ones (Tab. 3.1).
Table 3,1.: Mass loss and calculated penetration for copper and bronze samples (Rg7) exposed at 39 sites in 14
countries after 1 or 4 years respectively. From Stöckle et al,1993.
When considering the characteristic features of the corrosion layers obtained, 4 different cases are
usually observed (Fig. 3.2):
- dark smooth area found on rain-sheltered areas. They correspond usually to the original
surface. Oxide layer (cuprite Cu2O) combined with soot particles and chloride species
(atacamite Cu2(OH)3Cl) may be identified.
- Black crust found on rain-sheltered areas and for monuments older than several decades. In
addition to the previous compounds copper sulphates (brochantite Cu4(OH)6SO4 and
antlerite Cu3(OH)4SO4) are found.
- Light green areas on horizontal or inclined rain-exposed areas. Exposure to rain causes the
dissolution of the corrosion layers, sometimes exposing the underlying cuprite layer.
- Light vertical streaks on rain exposed areas.
Figure 3.2.: Sketches illustrating cross-sections of characteristic patina layers on outdoor sculptures. From Strandberg,
Different factors affect the presence of corrosion layers and their particular development. They are
presented below.
Corrosion also occurs on artificial patinated metal surfaces covered or not with a coating (wax).
Complex reactions may then be involved in addition to the basic principles described previously.
By Christian Degrigny and Dimitrios Charalambous
3.2. What factors affect the deterioration of outdoor bronze monuments?
Among the factors mentioned below, the acid rain and the application of graffiti are of particular
importance nowadays and bring new maintenance problems. In the following we concentrate on the
bronze part of the monument.
3.2.a. Techniques of construction
The alloy composition of the monument may influence the deterioration process. However, of more
importance is the structure of the bronze surface. A smooth surface that is chased and polished and
is free from pores and cracks best resists corrosion.
Iron parts in bronze sculptures may cause big problem due to galvanic corrosion. Large sculptures
are often constructed with an iron skeleton serving as an inner armature for the core, and smaller
sculptures occasionally have reinforcement in some weak parts. Iron bolts are sometimes used for
joining. Iron parts will rust and cause rusty stains. The large volume of the iron corrosion products
may also cause cracks in the bronze. Stainless steel is a better choice of material when new
constructions are made.
3.2.b. Artificial patination
The appearance of bronze may vary due to the artificial patination method used when the
monument was made. When a sculpture has been dark-patinated it may still appear darker for some
decades than if green patinated (this is attributed to both the composition of the patina and its
smoother surface). Other characteristic features due to patination method may be localized
corrosion. Patchy and cracked patterns on sculptures may also indicate an original patination or
surface treatment.
3.2.c. Humidity and climate
The humidity in the air is of great importance for the deterioration. Many corrosion mechanisms are
only occurring above a certain critical relative humidity (RH). About 70% RH is critical for many
corrosion processes on bronze. As indicated in table 3.2 the mean humidity in Göteborg and
Munich is close or above this critical humidity, while in Athens it is below. Consequently, the
corrosion rate is much higher in the humid Göteborg and Munich than in the arid Athens.
of rain
5.5 to 6
Table 3.2.: Climate and air-pollution values in the cities of Göteborg, Munich and Athens. Annual ,winter and summer
values are presented. (Munich source: Lufthygienischer Jahresbericht 1990 to 1999. Bayerisches Landesamt für
Umweltschutz 1999; Athens source: Greek National Observatory; and Göteborg source: Luftföroreningar i Göteborg.
Årsrapport 1997, Miljöförvaltningen, Miljö Göteborg (1998)
A marine climate is a strongly corroding factor for all metals. The salt that is transported with wind
and rain causes pitting corrosion of the metal. If the air is additionally polluted with sulphur dioxide
a synergistic effect occurs. Soluble compounds thus are formed resulting in weathering of the
In Nordic countries when marble is used as a material for the base, transformation of water in ice
may provoke damage of the material (cracking and deformation). As a result this process will
destabilise the bronze sculpture placed on it. Due to safety reasons, special attention of these
monuments is needed.
3.2.d. Outdoor pollution
There is a range of pollutants in the outdoor city air, which are crucial for the deterioration
processes on the bronze monuments. Mean values of some air-pollutants in the city air are shown in
table 3.2.
Sulphur dioxide (SO2) from the combustion of fossil fuel creates an acid electrolyte on the bronze
surface when water is present and forms the corrosion product brochantite (Cu4(OH)6SO4) by time.
This corrosion product gives the characteristic light green appearance of outdoor bronze sculptures
in cities. The SO2 levels showed very high levels in the 1970’s in many cities in Europe (one to two
magnitudes higher) but have decreased during the last decades, especially in the north of Europe
(Fig. 3.3). This has resulted in less amount of brochantite forming on bronzes nowadays.
Figure 3.3.: Historical emissions of sulphur dioxide in Europe between 1880 and 1990. Source: Mylona, S. Trends of
sulphur dioxide emissions, air concentrations and depositions of sulphur in Europe since 1880. Meteorological
Synthesizing Centre-West, The Norwegian Meteorological Inst., EMEP/MSC W report 2/93 (1993), p 22.
The corrosion rate of outdoor bronze monuments is closely related to the concentrations of acid
forming gases. In particular the amount of sulphur dioxide is correlated to the mass loss of outdoor
bronze sculptures as shown in figure 3.4.
Figure 3.4.: Dose-response function of unsheltered bronze exposed for 1, 2, 4, and 8 years. The material was exposed in
12 European countries and in the United States and Canada. Obviously, the damages follow an exponential curve.
Bronze alloy: G-CuSn7ZnPb (RG 7). From: Stöckle et al, 1993.
NO2 is a corrosive acid forming substance that shows synergistic effects with SO2 on copper and
bronze corrosion. The main source for NO2 emissions in city air is automotive exhausts. The
pollutant level is clearly related to the intensity of the traffic. In urban air, NO2 has not showed any
decreased trend during the last decades.
Ozone is a strong oxidant that also shows synergistic effects with SO2 and increases the corrosion
rate of bronzes.
Soot comes from incomplete fuel combustion and consists mainly of carbon. Soot is correlated to
SO2 emissions in a historical perspective and has simultaneously decreased in many European cities
the last decades. Soot mixed with corrosion colours the black rain shaded parts on bronze
Dust particles may be of many various kinds, sometimes protective for the material properties, and
sometimes damaging. An important aesthetic damaging factor is that dust deposited on a monument
covers and makes the surface of monuments dull so the artistic expression may be obscure. Dust
often contains sand and soil particles. Salt particles from the sea and from the dusty winter roads in
the Northern countries may deposit and be very corrosive. A thin layer of iron particles from tram’s
dust may deposit in bronze patina and may sometimes form a dense, smooth “yellow patina” that
has some aesthetic qualities and protecting properties.
3.2.e. Acid rain
Natural precipitation, rain and snow, is slightly acidic and pH in natural rainwater is about 5.6. Over
the last few decades, the acidity in rainwater generally has exhibited much greater acidity due to the
widespread occurrence of SO2 and NO2. This phenomenon has been particularly important in
Nordic countries as shown on figure 3.5. Today the acidity of rain in Europe is generally about 10
times higher than in the middle of the century and no decreasing trend is evident. The pH of rain is
consequently lower.
010 20 30 40 50 60
Bruno Stöckle & Andreas Krätschmer
Bavarian State Department of Historical Monuments
UN/ECE Programme on Effects on Materials
Bronze unsheltered
Exposure Time
1 year
2 years
4 years
8 years
Corrosion Mass Loss [g/m²]
Amount of Sulfurdioxide
in Air [µg/m³]
Figure 3.5.: Increase of precipitation acidity in Scandinavia between 1957 and 1970. The solid lines mark contours of
equal pH. From Wayne, 1985, p201. Source: Linkens, G., Chem. Engng News 54 (1976) 29.
The acidity in the rain may dissolve locally the patina that protects the bronze metal of the
monuments and initiate electrochemical corrosion processes between the bare metal and the
surrounding patina. This dissolution of the patina may also result in the loss of original surface
texture, e.g. tool marks on the surface.
3.2.f. The location in the city
The location of a monument is of certain importance for its condition. Sculptures in parks sheltered
from wind and traffic are better preserved than objects exposed to heavy traffic. Trees and bushes
absorb the air-pollutants and create a better atmosphere. Deep pits in the bronze surface created by
pitting corrosion are often observed on parts of sculptures close to the traffic.
Objects exposed to strong winds from the sea are characterised by being more light-green and
deteriorated on this side.
3.2.g. Use of the monuments
Many monuments have a practical function that may become a threat to the material properties and
intrinsic symbolic values of works of art. Water fountains, sculptural parts frequently touched by
man, and sculptures inviting and intended for children’s climbing, are example of monuments being
used. On the other hand traces of such practical use can be of importance for the true interpretation
of the image of the sculpture. Some modern artists appreciate children climbing and other use of the
monuments. However, artists sometimes have changed their opinion when the marked wear become
To a certain degree the touching, which implies polishing of the surface, preserves the monument.
The surface becomes smooth and maybe greasy which inhibits the corrosion. However, if the wear
goes beyond the cuprite patina and shows the bare shiny metal surface a prohibition to touching
should be considered.
Fountains sometimes suffer from thick deposits of lime from the pipe water that discolour and cover
the surface of the bronze. The aesthetic values certainly decrease with such crusts, however this
alkaline deposit may also protect the patina. Water rinsing the surface of a bronze may protect the
surface to some degree but at the same time mechanically wears the patina off. Some parts of
fountains, which are not rinsed, are constantly at very high relative humidity. This is a very
corrosive environment and pitting corrosion may be severe. Algae sometimes grow on the lime and
dust deposits on bronze sculptures.
Many monuments also have a practical function for animals. Birds love certain sculptures. Bird-
droppings may cause corrosion damage since their debris contain corrosive agents dissolving the
patina compounds. Greenish disfiguring deposits and streaks are formed on the bronze sculptures.
Spiders and other insects may also like to live in the monuments but do not cause any harm.
3.2.h. Vandalism
Graffiti and scrawl is a great problem in cities and has increased considerably in the last decade.
Vandalism may alter more drastically the appearance of an outdoor sculpture. The use of spray
paint or felt tip marker is a way of expressing public discontent towards government or society at
large. More radical forms of expression may be to use explosives or to physically remove the
sculpture or parts of it from its location. Here, such reactions may merit removing such a
monument, especially when it endangers people’s lives.
The bronze parts of the monuments are not used to be the most inviting to paint on, but the flat
bases, often in stone, seems to be inviting surfaces to write tags on. Paint products on bronze
surfaces may sometimes be impossible to remove without damaging the complete patina of the
object, especially when time has passed and the paint has been included in the corrosion products.
Graffiti paint should therefore be removed immediately. Professional guidance should be consulted
since acidic cleaning agents and hot medium pressure water may damage the patina.
Bronze is a rather hard and tough material that is not so easy to break without tools. However, there
are incidents where protruding parts have been broken off sculptures only by mans power. Since
many monuments are symbols with various meaning provoking vandalism sometimes occur. At
several occasions the head of the famous Copenhagen Mermaid have been sawed away. In Athens,
Monument has been several times the target of soldiers during the second world war who
shooted it (Fig. 3.6). There are also political actions aimed towards monuments symbolizing the
power. Some examples can be mentioned. The Peter I monument in Moscow was exposed to a
bomb attack 1997. The bronze Lions in front of the Norwegian Parliament House in Oslo were also
set in fire in 2001.
Figure 3.6: … Monument, by…, shooted with bullets during the 2nd war. Credit?
By Helena Strandberg
3.3. Problems that face outdoor bronze sculptures
The problems that face outdoor bronze monuments are essentially all man-made. While these
problems can be classified, they vary depending on the techniques of construction, location and
environmental setting of each monument, and subsequent documentation, treatment and
maintenance program in each city. For example, outdoor bronze monuments in Munich or Göteborg
tend to be more heavily corroded than in Athens. These cities in Northern Europe have heavier
rainfalls and are more humid than a country like Greece, which is warmer and more arid in its
climate. In today’s polluted environment, rain in most rural areas in Europe is acidic, which results
in further stimulating corrosion of outdoor bronze metal. However, outdoor bronze monuments in
Athens suffer more from vandalism than in Munich or Göteborg, most likely due to public
insensitivity towards the history of their city’s monuments. The public may be uninformed of both
the historical and artistic significance of these works of art.
Acid rain and vandalism are man-made factors that alter visually the appearance of bronze
sculptures and disfigure them. Pollution such as acid rain changes slowly the colour and texture of
the original surface. Unfortunately, the colour changes are not uniform, so that on an artificial black
patina surface, streaks or patches of light green may appear, which are unpleasing to the eye, and
affect the artist’s original intention. This phenomenon characterises particularly monuments of the
last decades. This corrosion may also cause serious damage to changes in the surface texture. The
corrosion layers that form with time may hide or distort surface details, such as tool marks that are
signatures of the artist and craftsman.
Many factors influence the extent of deterioration caused by acid rain and vandalism to such
monuments. For example, the shape of the monument or holes located in metal due to casting
methods may result in more accumulation of water in certain areas of the sculpture. Improper
materials used or unrefined finishing in the techniques of construction of a sculpture can lead to
unpredictable problems when they come in contact with water.
Also, monuments located in hidden and isolated areas that can be reached by the public tend to be
easy targets for graffiti. Lack of urban planning in proper placement or an uninformed public as to
the historic significance of a monument increases the chances of monuments becoming attacked by
Finally, the biggest problem that faces outdoor bronze monuments is a lack of funding and proper
planning to protect them. Some city officials believe that caring for outdoor bronze monuments is
similar to cleaning a sidewalk. Untrained personnel who do not have knowledge, experience, or
judgment in the conservation of such objects have caused much damage to such works of art.
While it would be unthinkable to use untrained workers to restore or even touch a museum object,
in some cities it is common practice for such workers to handle our monuments. Furthermore, some
cities may sporadically invest in restoring some of its outdoor monuments, without even
considering investing long-term in maintaining them.
By Vasilike Argyropoulos
3.3.a. Athens: vandalism but slight corrosion problems
There are around 63 outdoor bronze monuments in Athens. A conservation survey, which means
documenting the location, historical information, and condition of the monument, has recently been
carried out for all the monuments. The results show that around 20% have graffiti on the metal
surface of the sculpture either in the form of paint or felt tip marker. Around 15% have graffiti
problems on the marble base of the monument. A few monuments have missing parts, due to
The annual SO2, NO2, and soot values in Athens are more than double the values of Göteborg or
Munich (Tab. 3.2). One would expect with such high pollution levels for outdoor bronze
monuments to be in worse condition than those in Munich or Göteborg. On the contrary, due to the
low annual rainfall and relative humidity, outdoor bronze monuments corrode at a much slower rate
than in northern European countries. Nonetheless, monuments that have been placed outside for
more than 10 to 15 years show visible signs of alterations on the surface of the metal. These
alterations are in the form of streaking or light green patches, which are disfiguring to the original
appearance of the sculpture. Older monuments around 100 years old, such as the Kolokotronis
monument, show signs of black crusts on the surface of the metal, as well as streaking and light
green patches.
By Vasilike Argyropoulos
3.3.b. Göteborg: sculptures in a rough marine environment
The outdoor monuments in Göteborg face a rough humid and corrosive environment. The city is
situated on the west coast of Sweden and has a strongly corrosive climate due to the proximity to
the sea that brings sea salt by the western winds, high humidity in the air, pollution from heavy
traffic and industry, and an acid rain falling. These factors affect the outdoor monuments in such
way that they will corrode faster than e.g. in Athens that has a dryer climate or in Munich that has
an inland climate. Therefore the monuments may turn green in a few decades in Göteborg and this
is the way the people in the city are used to see the monuments. However, the green patina and also
the black soot crust on old monuments is nowadays dissolving by the acid rain. This causes the
streaked appearance on sculptures. The patina on rain-exposed parts of the sculpture become
weathered and destroyed.
In Göteborg, the sculptures from the 1940s and 1950s appear to be in a rapid change. They show
evident colour contrasts between dark and light green areas and distinct vertical streaks caused by
the rain. Orange or brown areas also occur indicating the leaching of patina compounds.
Older sculptures, from the 19th century or from the beginning of this century, exhibit considerably
thicker corrosion product layers. In some cases the sculptures appear predominantly green. Thick
black hard crusts are evident in rain-sheltered areas. The green discoloration on adjacent stone bases
of older sculptures, especially when they are made of marble, also indicate the dissolution and
washing-out of copper compounds, especially on marble bases (see figure 1.8 of Gustav II Adolf in
By Helena Strandberg
3.3.c. Munich: a typical case of western Europe large city
Damages on historical monuments have to be interpreted with respect to the environmental situation
in the surrounding area. Germany has a continuous weather and pollution monitoring since about
1950. As there were no suitable methods before that time, those measurements were only done
sporadically. Like in other countries in western Europe the SO2 pollution has decreased. In East
Germany the situation has improved most.
Munich is a large city in the south of Germany that nowadays has a moderately corrosive climate.
Outdoor bronze monuments have to resist to influences by heavy traffic and acid rain. Fountain
sculptures are exposed to water that contains a considerable amount of calcium carbonate as well.
This often causes the formation of thick crusts on the sculptures. The colour changes to light grey.
The visual appearance and changes of the visual appearance of Munich’s outdoor bronze
monuments is similar to the situation in Göteborg. First the monuments turn to dark-brown or black,
then acidic attack begins to undermine the black surface, a process which is being signalised by the
formation of green corrosion products. This lasts at least a few decades. It is the typical fate of
bronzes of the 19th century.
More than 75% of the Munich bronze monuments are situated in or near the city centre where the
amount of SO2 has been 20-40 µg/m3 in 1967. The majority of bronze monuments from the 16th-
18th century are situated in inner courtyards but still in vicinity to main streets. About 25 big bronze
monuments are standing directly at streets. Most big bronze monuments of the 19th century are
situated on squares with high traffic in the city centre where they face the main sources of air
By Anke Doktor and Martin Mach
Conservation Strategy
4.1. General approach
4.1.a. Planning conservation
Professional conservation practice presumes an understanding of many factors. Among these are the
intent of the artist, considerations of the values that people attach to the objects, and the use of the
monument. Moreover, the practice assumes a sound knowledge of the effects of time on the
material properties, its implications for the object and various treatments according to the principles
established. However, in many cases decisions concerning selection of conservation treatment often
take place without a professional conservator involved in planning and/or execution of conservation
4.1.b. Ethical considerations
Standards of conservation have been developed to guide intervention for all kinds of cultural
property and are found in some of the recent documents including: the AIC document (revised
1979), the Venice Charter (1964; revised 1978), the Burra Charter (Australia ICOMOS 1988), and
the Nara document (1995). All these documents identify the conservation process as one governed
by absolute respect for the aesthetic, historic, and physical integrity of the object with a high sense
of moral responsibility. This implies obligations that fall into the following categories:
to perform research and documentation, i.e. to record physical, archival, and other
evidence before and after any intervention;
to respect cumulative age-value, i.e. to acknowledge the work as a cumulative physical
record of human activity embodying cultural values, materials, and techniques;
to safeguard authenticity, i.e. to respect and understand the values attributed to the
heritage. However, it is not possible to base judgments of value and authenticity on absolute
criteria, since judgments may differ from culture to culture, and even within the same
to perform minimum reintegration, i.e. to re-establish structural, aesthetic, and semiotic
legibility with the least possible interference with the original;
- to perform interventions that will allow other options and further treatment in the future.
4.1.c. Documentation
Documentation should always be performed before, during and after any intervention. This includes
- photo documentation;
- historical research of the object;
- recording of the condition of the object, e.g. colour, patina cross sections;
- definition of the “original surface”;
- recording of damages;
- analysis of the object, e.g. corrosion samples, alloy composition;
- analysis of the environment;
- analysis of causes of damages;
- documentation of all measures performed including method, material, products, and chemicals.
To find the causes for the actual condition historic research is necessary. Analyses of corrosion
samples and e.g. alloy composition may reveal causes for deterioration and information relevant for
the history of technology.
This documentation is essential to establish the condition report and define the conservation plan.
4.1.d. Choice of interventions
Interventions may be exercised in different ways to preserve qualities of significance. They should
be minimised as they may always involve some loss of value. Different degrees of intervention are
identified which can take place separately or simultaneously in conservation treatment. They are
presented below:
Prevention of deterioration may include planned measures after diagnosis, e.g. to reduce
atmospheric pollution. Preventive measures for new sculptures may be the consideration of
appropriate patination methods for sculptures and locations for inauguration. Regular professional
inspection and maintenance plans to prevent the development of undesirable changes are other
preventive measures.
Preservation signifies the effort to keep cultural property in the existing state, e.g. by
maintenance, including superficial cleaning of surface dirt and repair. By removing corrosive agents
such actions may preserve sculptures from deterioration.
Consolidation is the addition of supportive materials to ensure structural integrity. This includes
application of coatings to preserve patina of sculpture from corrosive atmosphere and acid rain, e.g.
by waxes. Preservation by consolidation may be executed with the aim to "freeze" objects in the
existing state with use of conservation materials regarded as "reversible", and sometimes with
material that is supposed to be long-time durable. Retreatable methods, e.g. the use of waxes, allow
future treatment and are of considerable significance for architecture and outdoor monuments in
corrosive environments.
Restoration is the renewal of material components, which implies the revival of an original
concept or legibility of an object, e.g. in cases where random coloration of corrosion and crusts
visually destroys sculptural form and reading of surface texture. This may include total or partial
removal of corrosion products, mechanically (e.g. by metallic wool; abrasive pads; abrasive tools;
peening with sand, glass beads or granulates of walnut shells; or by ultra-high-pressure water) or
chemically (e.g. by chelating agents or acids). After removal of corrosion products, repatination of
the sculpture may be performed with chemicals. Restoration is often a controversial issue. The main
motives for such actions often are based on aesthetic and/or functional considerations, and not
primarily on efforts to reduce the rate of decay.
Reproduction implies copying an extant artefact, e.g. when the original version has to be moved.
Such protection of an authentic work may be the case for sculptures of exceptional value, or when
an object is threatened by the surrounding environment.
- Reconstruction must be based on accurate documentation. A missing part of a sculpture may be
reconstructed since it sometimes is necessary in order to re-establish visual appearance and
meaning. However, it should neither replace nor compete with the original work or with the
conservation process, but be an integral part of the object.
4.1.e. Preventive strategies
- Professionals should be consulted before any intervention on outdoor art.
- Education and supervision in conservation for all professionals involved in the handling of
outdoor public art is necessary.
- Professional inspection of outdoor art should be performed regularly.
- Maintenance plans should be designed and implemented to prevent the development of
undesirable changes.
- Conservation should be considered already at the commissioning of new art-works. The
construction, choice of material and patination method could be discussed with craftsmen and
artists before the construction begins to avoid safety, structural and aesthetic problems in the
future. The location of inauguration could also be considered in this context.
4.1.f. Treatment
Minimal and retreatable intervention performances should preferably be chosen and strong
measures such as restoration avoided if possible. However within this range there are many ways to
treat the objects.
When minimal intervention is performed the patina on the sculpture is respected as an integrated
part of the object and will never be taken off to the bare metal. However, deposits of soot and dust
that cover the surface and may be corrosive is removed, as well as some corrosion that disfigures
the original surface texture. The aim is to clean from dirt, uncover the original surface and
strengthen the patina by making it denser e.g. by polishing.
The conservators methods for cleaning include low-pressure water, nylon brushes, and scalpels.
Chemicals are used selectively with great care with the risk to stimulate further corrosion. The use
of harder methods like blasting with walnut shells and medium-pressure water are sometimes used
by conservators but may remove some of the light green patina. Sandblasting has to be avoided
because even the finest and softest material removes the green patina completely while the brown
cuprite patina is more stable.
The cleaning is restricted to the controlled removing of crusts of dirt and sometimes lime (in the
case of fountain sculptures) that lies above the original patina. As already said the aim of a bronze
conservation is to maintain the ageing value and not to uncover the shiny metal surface. The
disturbing layers are removed with stainless steel scalpels. If there are brittle layers and thick lime
crusts, vibrating tools can come to use, but only if the crusts can be removed in flakes. It may also
be necessary to dense the rough crusts with rotating synthetic brushes. Laser cleaning is being
discussed right now but its use is still far away from the practise routine work.
A wax coating may have a positive influence on the visual appearance because colour contrasts
caused by corrosion will be reduced and the surface gets a silky metallic shine. One question may
be why not covering the whole sculpture with a modern kind of synthetic coating? There are many
disadvantages for those methods. First of all the metallic character of the sculpture will be reduced
and the sculpture will achieve a shiny, more plastic look. The lacquer does not disappear by
weathering but stay on the surface in that partly disappeared state, which makes the bronze look
grey and neglected after a while. A partial renewing of the coating is neither possible. Lacquers
have been developed for outdoor copper and bronzes (Incralac, Ormocer) but they have not found a
large application in conservation.
Instead, the microcrystalline waxes are mainly used for conservation today and have been optimised
for metal conservation. Chemically, they are to the largest part paraffin waxes consisting of long
chain and sometimes branching hydrocarbons. They have a good water resistance but allow oxygen
to diffuse through. The melting point of the wax should be high enough so the wax does not get
sticky under sunlight. Beeswax is another wax that has long been used in conservation. It is simpler
to apply but may become soft and sticky under sunlight and is more rapidly worn off.
The conservation with wax has the disadvantage that it cannot stand raining as long as a lacquer. On
the other hand it remains at least for two years (in Göteborg and Munich) on the exposed parts and
clearly longer on sheltered parts. Wax coatings can be renewed partly without problems and if
nobody cares about the coating they simply disappear through raining without leaving traces or
damages. Last but not least they adjust the colour contrasts and to some degree restore the lost
metallic look.
In most cases the restoration measures concerns only the outer surface of the sculpture, but
sometimes it can also be necessary to have a look on the interior parts, in particular if there are rust
streams or cracks visible on the surface. These damages are often caused by an iron construction
lying inside the sculpture. When the iron is corroding it expands its volume and may break the
bronze structure. When severe interventions have to be done, like restoration of structurally
damaged sculptures, reconstructions, and new joints for sculptures, conservation professionals
should always be consulted.
By Helena Strandberg
4.2. Cases studies
In the following we present some case studies that illustrate the general strategy chosen by the three
partners of the European project. Some of the partners, from Munich and Göteborg, have a large
experience in the conservation of outdoor bronze monuments and used then well defined
procedures. Athenians partners that began in the field benefited from the experience of their
colleagues. The conservation of the Kolotronis monument in Athens is taken as an example and is
described thoroughly. Strategies for other monuments are described more briefly.
4.2.a. Monument in Athens
Two monuments were considered in Athens, Kolotronis monument and the bust of Lekaditis.
Theodoros Kolokotronis
Figure 4.1.: Theodoros Kolokotronis monument in front of the Old Parliament building in Athens. Credit?
The sculpture of Theodoros Kolokotronis located in front of the old Parliament building in Athens
was made in 1900 and erected in 1904 (Fig. 4.1). Kolokotronis or the ‘Old Man’ as he is
nicknamed by Greeks was the beloved war hero of the Greek War of Independence in 1821, and he
inspires and unites Greek people. The sculpture was created by Lazaros Sochos, who was one of
the most distinguished Greek Sculptors, and has won international awards. The statue was
manufactured by L. Gasne, successor of Thiebaut Frères Parisian foundry.
There are no records that the monument has ever been treated before by conservators, although
there are testimonials by museum employees located next to the monument that measures to clean
the monument have taken place in the past. It was chosen for our campaign of “Protect our Outdoor
Bronze Monuments”, because of its importance to the Greek people and no thorough examination
exists describing its details of construction or its current condition.
The monument stands around 9m from the ground on a marble base that has bronze relief
representations of war scenes on either side of the base also created by Sochos in 1895 and 1897
(Fig. 4.2).
Figure 4.2.: Bronze plaque made in 1895 and located on marble base, which depicts Kolokotronis with his raised
sword leading the Greek troops, and successfully fighting off the Turks. Sochos is also depicted among the Greek
troops. Credit?
The base was designed by the architect Alexander Nikoloudis and made by the sculptor Ioannis
Karakatsanis using two types of marble, Kokkinara and Pentelic for the three levels of the base.
Further inspection of the monument indicates that it was cast in 5 separate pieces, the helmet, the
upper body, the lower body with horse and base, the head of the horse, and the tail of the horse (Fig.
Figure 4.3.:ndicates the soldered join of the Horse’s tail to the body of the horse. Credit?
The horse’s reins, gunpowder holder, and straps on Kolokotronis were added to the monument as
separate pieces. All pieces were soldered in place and/or held together with screws. For example,
the helmet has 3 screws (at both sides and back of the head), and has stucco covering the entire
periphery of the join of the helmet to the head of Kolokotronis (Fig. 4.4).
Figure 4.4.: Shows the stucco that was used to help secure the helmet to the head of Kolokotronis. Credit?
Location of
tail and
Location of
join of
helmet to
head using
This unrefined join of the helmet stands out to the rest of the sculpture, where the soldered parts can
barely be identified due to its fine craftsmanship. Closer inspection of the helmet provides further
evidence as to why Lazaros Sochos produced such a rough join on the helmet. An epigraphy was
found behind the tail of the helmet, which reads “Despite Soho’s will, my Kolokotronis wears again
the helmet, Paris 190(9 or 2?) (Fig. 4.5). A mould of the epigraphy was taken and using a scanning
electron microscope it was possible to determine that the last digit in the date is actually 2. (Fig.
Figure 4.5.: Indicates the location where Sochos placed his objection to the placement of the helmet on Kolokotronis.
Figure 4.6.: Mould of the inscription at the back of the helmet. Credit?
The epigraphy on the helmet makes it clear that the artist’s intention for his sculpture was
overridden by the desire of a committee, who commissioned the work.
The bottom part of the sculpture was cast including a bronze base with decorative relief. The bronze
base has four bolts that secure it to the marble base. The sculpture shakes when a hand applies even
slight pressure; such elasticity is needed for the bronze sculpture to prevent it from cracking at the
Scientific examination of the monument revealed that the chemical composition of metal to be Cu
89.5%, Zn 4.9%, Sn 5.1% on the heel of the right leg of Kolokotronis and with the same
composition on the front right leg of the horse. This alloy is not the one which resists the best in
corrosive atmospheres but due to the dry climate of Athens, the corrosion of the monument appears
to be limited compared to what could be found in Göteborg and Munich.
Techniques to determine the internal structure of the monument, such as use of an iron skeleton or
lead metal were not applied, because of the location of the monument (in a central location with
passers-by throughout the night and day so that it was not be safe to use low levels of irradiation to
identify the internal structure). However, our discussions with today’s Greek sculptors lead us to
believe that the horse’s legs were cast hollow and were later filled with lead metal, so as to support
the sculpture.
It was common for sculptor’s of this period to artificially patinate with sulphur liver the bronze
monument to give a shiny black appearance. Examination of the bronze monument, in locations
that are sheltered from rain reveals a dark black colour on the surface, most probably the original
surface. The horse’s body has been chased, which provides a rippling reflection of light as opposed
to the smooth metal surface as in the face of Kolokotronis, which provides a steady reflection of
Condition report
The bronze statue
The original appearance of the monument has altered after 100 years of exposure to the pollution of
downtown Athens, with its location in one of the busiest commercial streets in the city. The
sculpture is covered with dirt and debris from the surrounding environment. The top of the sculpture
is light green where it frequently comes in contact with rainwater (Fig. 4.7). Other locations have
signs of disfiguring streaking, caused by the run-off of rainwater or acid attack through the
condensation of water vapour (Fig. 4.8). In locations that water does not frequent, dirt and debris
has accumulated, and slowly formed thick hard black crusts (Fig. 4.9). Scientific analysis of the
corrosion layers revealed that the black crusts are made up of different mixtures of gypsum, quartz,
calcite, atacamite and crystalline carbon due to soot. The presence of soot particles gives the crust
its black colour. This is typically found on bronze monuments of such age.
Examination underneath the crusts revealed the presence of a red-brown layer, most probably
cuprite, a stable corrosion product. Other corrosion products detected were atacamite, copper
sulphate hydroxide, copper sulphate hydrate, all typically found on outdoor bronze monuments in
Europe. Malachite was also detected, which is more uncommon to find on outdoor monuments.
Figure 4.7.: Green patches on Bronze Sculpture. Credit?
Figure 4.8.: Streaking on Horse’s body. Credit?
Figure 4.9.: Signs of thick black crusts on Bronze sculpture. Credit?
A few very minor cracks were located in the monument at join (top of horse) and at the side of the
horse. Also, two screws were missing from the reins of the horse. Finally, many scratches possibly
made with a scalpel were found at the sides of the horse and underneath horse’s stirrup. This leads
us to believe that someone had tried to clean the sculpture before (Fig. 4.10). Otherwise, such
damaging marks may have occurred when the monument was moved from the top of Kolokotronis
Street to its current location in 1954.
Figure 4.10.: Evidence of scratches on bottom of stirrup. Credit?
The marble base
The marble base has many conservation problems caused by the polluted environment and
vandalism. The top part of the base with decorated relief has the most problems with areas of thick
black crusts (Fig. 4.11), cracks, and even missing sections of the decoration (Fig. 4.12). Scientific
analysis of the black crusts indicates that it contains gypsum and soot. The cracks and green stains
have formed from run-off of water from the bronze monument (Fig. 4.11). Many locations in
decorated sections of the marble base have a sugary appearance, which reduces the decorated relief
representation. Also, in many sections on the base exist purplish black stains caused by
microbiological attack to the marble. A more frustrating problem is the disfiguring graffiti in front
of the base at the epigraphy (Fig. 4.13). Felt tip marker has been used to write two large words.
Previous measures were taken to remove this graffiti, which unfortunately etch the surface of the
marble, which was later disguised using white paint and gesso. Finally, careful examination has
revealed that most probably the marble was coated with either a wax or oil from a previous
treatment for its protection.
Figure 4.11. Black crusts and green stains on upper part of marble base. Credit?
Figure 4.12.: Cracks caused by water run off. Credit?
The bronze plaques were in excellent condition when compared to the sculpture or the marble base.
Conservation plan
The conservation treatment was conducted in two phases, first the bronze sculpture and then its
marble base with side bronze plaques. The first approach was the following: removal for the
sculpture and the base of external material that may continue to actively corrode or deteriorate the
metal or marble ; further cleaning may be conducted to bring out decorative details that are lost in
the corrosion layers ; touch ups to the colour or restorations for missing parts conducted to improve
the aesthetic appearance of the monument and finally, application of a protective coating to help to
slow down any further alterations to the surface appearance and to allow for easy removal of future
applications of graffiti.
Conservation treatment
For the bronze sculpture, all dirt, debris, soot, and other soluble corrosion products was removed
with soft filtered water under pressure and a mild soap, used commonly in metals conservation. As
much dirt was removed as possible without harming the metal surface or the patina underneath.
Then mechanical cleaning using a scalpel and other tools was conducted to remove black crusts to
reveal decorative detail. Care was taken not to remove the stable cuprite layer underneath the black
crusts. In some locations, it was decided not to remove the black crust at all, because revealing the
cuprite layer on large surfaces, such as the side of the horse’s head would alter considerably the
colour of the darkly patinated surface. This followed our decision not to use any chemicals to clean
or tone down variations in colour on the metal surface. Such a decision was necessary, because
once the scaffolding is gone, the sculpture cannot be easily approached by the conservator to be
assured that with time the surface is not affected by possible residual chemicals that may have
remained on the surface after treatment. Also, the public from below cannot see with great detail
slight variations in surface colour. After mechanical cleaning, the surface was rewashed with soft
filtered water and degreased using acetone. A protective microcrystalline wax coating (TeCero
3534F, Tromm Company) was applied by heating the metal surface to around 100°C. The wax
coating also toned down the variations in colour, and gave the surface a darker appearance than
before, as was the artist’s original intention. The bronze plaques on the base, due to their excellent
condition, were simply washed and waxed as described above. No further mechanical cleaning was
For the marble base, any disfiguring variations in colour caused by black crusts or green stains is
easily detected by passers-by. Thus, dirt, debris, black crusts, green stains, and graffiti had to be
removed as much as possible without harming the marble. First dirt, debris, and other soluble
products were removed with soft water saturated with calcium sulphate (explain why). For efficient
treatment, it was deemed necessary to remove black crusts and green stains using pastes with
absorbent clays (which chemicals in the paste?), which were thoroughly rinsed off with filtered
water. This treatment was time consuming, since it was conducted in stages with careful
examination to ensure the marble was not affected. Some mechanical cleaning with scalpel for
careful in-depth probing and removal of the black crusts was necessary in the decorated relief. Then
the decorative relief was consolidated. It proved impossible to remove the purplish-black stains
caused by biological attack, which could only be toned down in colour.
More problematic was the removal of the graffiti made with felt tip marker, which was located in a
visible location and disfigured the monument. The felt tip marker had penetrated the porous surface
of the marble after many years. The only recourse was to destroy the marker with a paste
containing a chlorinated solvent. This paste did not completely remove all traces of the marker.
After consultation it was decided not to disguise the remaining graffiti, so that the public may
become sensitised to the destructive and the permanent affect of graffiti. Then the entire marble was
covered with a protective coating of anti-graffiti product, which contains wax, so that any
subsequent vandalism with paint or felt-tip marker can be more easily removed. The epigraphy both
on the front and back of the base was retouched only with black paint.
Finally, it was decided not to replace the missing parts in the decorative relief. Fitting in new pieces
of worked marble in the decorated sections, would require that some of the original marble would
have to be removed. The missing parts were deemed not to affect the overall aesthetic appearance
of the base, and thus it was decided to not restore these sections.
The final appearance of the monument after treatment can be seen in the Figures below (which
Lekaditis bust
A total of 12 conservators at different times worked on the monument for an operation that lasted
just over 2 months. This does not include the scientists, historical researcher, photographer, and
videoscoper who aided in the documentation and analysis phase of the conservation work. Also,
technicians from the Municipality of Athens were responsible for raising the scaffolding and
ensuring safety in operating the electricity and water on-site. The total cost of the operation was
around 35.000 Euros without profit. Do such operations mean that the monument will not have to
be maintained? It will be necessary to reapply the protective coatings both on the bronze sculpture
and marble base every 3-5 years based on the experience in Germany and Sweden, at a much lower
cost to that of the original treatment. Such preventive measures will ensure minimal changes to the
surface appearance of the bronze and marble, and will prevent subsequent retreatment at a later
The conservation treatment of the Kolokotronis monument made front-page news, and appeared
several times on television new channels in Greece. The public frequently stopped the conservators
at work to shout up words of support and to find out more information about the project. The
public’s message was clear; Athenians adore their ‘Old Man’, and very much want to keep him
bright and shiny. Our public campaign to Protect our Outdoor Bronze Monuments has succeeded.
By Vasilike Argyropoulos
4.2.b. Monuments in Göteborg
In Göteborg, three bronze sculptures were selected for this project. The largest sculpture was “The
knife-wrestlers” and the treatment will be described below while the two smaller sculptures “The
haze” and “Wadman” are only shortly presented.
The knife-wrestlers
History of the monument
The Swedish sculptor Johan Peter Molin (1814-73) first exhibited “The knife-wrestlers” in Paris
1859 (Fig. 4.). The sculpture is from the National Romantic period, a part of the Nordic history
when the Nordic myths and tales inspired the art. In “The knife-wrestlers” Molin made a dramatic
interpretation with realism in figures and movements.
Figure 4..: ”The knife-wrestlers” before conservation. The whole sculpture is 3.43 m height and the postament is 1.97
m in length. The second relief is viewed from this side. Credit: Claes Jansson.
The original sculpture exhibited in Paris was made of zinc and was painted to achieve the
appearance of green bronze. After exhibition in Paris and London it arrived in Göteborg and was
placed outdoors in the city. The bronze surface had to be regularly repainted and by time the thick
layers deformed the sculptural details. This aesthetic problem raised a discussion in the community.
Finally in 1912 funds were raised for casting a new copy of the sculpture, this time in real bronze.
In 1913 the new bronze sculpture, weighting 1400 kg, cast at Otto Mayer’s foundry in Stockholm,
arrived in Göteborg by train.
The tale on the monument
The monument (Fig 4. and 4.) shows two muscular men with knifes in their hands fighting against
each other when linked together with a belt around their waists. This was an old Nordic way of
fighting described in the tales.
Figure 4.2: Before conservation. Close-up of “The knife-wrestlers”. Credit: Claes Jansson.
The four reliefs around the postament and the runes tell more of the tale. Ragnar and Björn are
foster brothers, now Vikings in the West. When they return home they both fall in love with Gerda,
a beautiful woman living in their house. The love slowly tears the bond of brotherhood apart. The
first relief shows when Gerda gives mead to the brothers that are tense and wordless. The fight is a
fact when Björn break the silence and stretches his arm towards Gerda (relief two, fig. 4.1). In the
third relief (Fig. 4.) Gerda is pleading for the brother’s lives. The end of the tale is a tragedy where
the girl grieves the dead men and their friendship.
Figure 4..: Before conservation. The third relief on the postament of “The knife-wrestlers”. Credit: Claes Jansson.
Construction and original appearance
The whole monument is 3.43 m high and the size of the men is somewhat less than natural man
size. The bronze is cast in many pieces that are joined together. The composition of the bronze is
given in table 4.1. It can be classified among the corrosion resistant alloy. When the whole
monument was lifted for transport to the conservation workshop the inside revealed some joints
showing folds with screws (Fig 4.).
Table 4.1.: ICP analysis of “the knife-wrestlers” by Josef Riederer, Rathgen-Forschungslabor, Berlin, Oct.2001.
Figure 4..: Interior parts of “The knife-wrestlers”. The ceiling of the postament and the runes above the relief are
viewed. The bronze peg in the middle is one of only two joins between the upper part of the sculpture and the
postament. Photo: Helena Strandberg.
Originally, the surface on the sculpture was black, shiny and smooth, carefully chased and
artificially patinated with sulphur liver before the inauguration in 1914. The appearance has
changed during the 20th century due to the polluted environment and activities around the sculpture.
Today, many patches from repairs of casting defects appear on the surface. These were not visible
originally due to the artificial patination but have appeared by time in the corrosion layer.
The monument and the surrounding
The sculpture is placed in the busy central public commercial street in Göteborg where many
people, as well as cars and trams, are passing day and night. It is viewed from a close perspective
and is frequently touched. Events often occur around this sculpture and the postament is used as a
shelter and background for various activities that leave traces on the monument.
Condition and causes
Before conservation, the sculpture appeared much dirtier and more corroded than others from the
same age in Göteborg (Fig 4.1, 4.2, 4.3). The legibility had decreased due to thick deposits of soot,
dust, scrawl, sticky stuff and corrosion, especially on the postament. Traces of white paint were
visible originating from an occasion of vandalism in the 1960’s were all the sculpture was covered
in paint.
The original dark smooth surface, viewed on old photos, that was probably dominant until the
1970’s, was not evident any more. Instead, the sculpture appeared mainly light green and streaked
before conservation. Thick black rough corrosion crusts also covered many parts sheltered from
rain. Under these crusts, corrosion was active in pits with green corrosion. Analysis confirmed
(nantokite beneath the black crust) that the sculpture suffered from bronze disease that is caused by
high amounts of chlorides.
The fourth relief heading towards the street had a damaged porous surface with no original patina.
The sculpture probably have been blasted or treated with acid previously when cleaned from scrawl
and paint.
The largest problem though was a beige opaque and rough concrete-like deposit all over the
skyward surfaces on the monument, which was very difficult to remove. X-ray diffraction analysis
showed that the deposit contained a range of concrete mineral fillers (albite, quartz, high-temp
quartz, gypsum from calcite, and microcline), which confirmed that the deposit was concrete
probably originating from construction work in the proximity.
To sum up, the bad condition of this sculpture is mainly caused by its very exposed position to
traffic and diverse human activities. Moreover, it has not been sheltered when constructions have
been built in the proximity and not been cleaned in a proper way previously.
Conservation plan
The purpose of the conservation treatment was:
- to respect the aesthetic, historic, and physical integrity of the object according to the
conservation ethics.
- to perform minimum intervention, i.e. not remove the ”original patina” and preserve the
light-green corrosion layer on the etched rain-exposed parts.
- to remove disfiguring deposits of concrete, soil, sand and soot and some corrosion
- to protect and consolidate the patina layer with a suitable wax.
- to integrate colour contrast by the wax treatment.
Conservation treatment
The cleaning included removal of deposits, scrawl, paint and some corrosion; with water, soft
brushes and scalpels. On some smaller parts chemicals were used. The green patina on the etched
rain-stroked parts, protecting the metal was preserved. In some parts the green layer was removed to
uncover the black original patina that was found closest to the metal.
The thin hard concrete layer deposited on the surface, could only be removed with effort by
scalpels. This was a very time consuming treatment and therefore only some important parts were
cleaned this way.
Afterwards, a thin wax (TeCero 3534F, Tromm Company) layer was applied for aesthetic reasons
and to protect the surface from the rough outdoor environment. The wax paste was applied with
brushes on a heated bronze surface. Figures 4… show the sculpture and some details after
Figure 4.: ”The knife-wrestlers” after conservation. Credit: Claes Jansson.
Figure 4.: After conservation. Close-up Close-up of “The knife-wrestlers”. Credit: Claes Jansson.
Figure 4.: After conservation. The third relief on the postament of “The knife-wrestler”. Photo: Claes Jansson.
“The Haze”
This sculpture was first made in gypsum in 1885 by G. Lindberg. It was later cast in bronze 1914
and placed in a park in Göteborg. The sculpture was probably patinated green originally.
Figure 4..: “The haze” before conservation. Credit: Claes Jansson.
The patina on “The Haze” was mainly smooth and light green but etched in a cracked pattern on
rain-striking parts (Fig 4.). In some parts there was a yellowish smooth beautiful patina. The surface
was very gently washed not to destroy the green patina, and the black crust was cleaned with a
scalpel, before the patina was consolidated with wax (Fig. 4.).
Figure 4.9.: “The haze” after conservation. Credit: Claes Jansson
Wadman bust
The bust of J. A. Wadman is one of the oldest outdoor bronzes in Göteborg and was sculptured by
J. P. Molin 1969. It was treated about the same way as “The knife-wrestlers” though it was much
easier to clean since it had always been placed in a park shielded from traffic.
Figure 4.1..: “Wadman” before conservation. Credit: Claes Jansson.
Figure 4.11.: “Wadman” after conservation. Credit: Claes Jansson.
By Helena Strandberg
4.2.c. Monuments in Munich
Due to the complexity of the monument considered, the Amazone, no other monument was treated
during the project.
The Amazone
The Amazone was cast in 1935, unveiled in 1936. These dates were unknown before the beginning
of that project. Photographs of the foundry with the Amazone appearing out of the casting mould
have been found since. The monument simply represents an Amazone sitting on horseback. It is a
full-size reproduction of a smaller bronze Amazone by the famous Munich painter Franz von Stuck
which had been produced short before 1900.
With the Amazone, Franz von Stuck followed a popular style of fairy-tale human-animal creatures
which was very much appreciated by the Munich citizens. More than 20 of those small Amazones
are known. The big Amazone we are considering here was cast after Stuck’s death and put in front
of the Villa Stuck posthum.
Figure 4.?.: The Amazone sitting on horseback, before restoration. Credit Bavarian State Department of Historical
The Amazone has been selected for this project because of its special colouring consisting of
pigmented and gilded layers. Red pigments are found on the Amazone’s hair and gilding is used on
the helmet (Fig. 4. and 4.) and the horse’s mane and tail. In Germany colouring on outdoor bronze
monuments is rare to find.
Figure 4..?: The Amazone in front of the Villa Stuck Museum, Munich, in 1990. Gilded and painted areas are visible.
Credit Christian Gruber.
Fig. 4.?: Cross-section through an embedded paint layer sample from the red hair of the Amazone. Maximum layer
thickness 150
m. Credit Martin Mach.
The corrosion of the sculpture looks similar to other bronze monuments in Munich which normally
appear with a green and black patina. The heavy corrosion of the Amazone is to some part due to
the alloy (Tab.4.2) which is not very corrosion resistant (due to its rather low tin content) and due to
the situation close to a big street with about 50.000 vehicles passing by per day.
Table 4.2.: ICP analysis of the Amazone by Josef Riederer, Rathgen-Forschungslabor, Berlin, Oct.2001.
As expected the green areas (streaking) of the surface are found on exposed parts of the sculpture
whereas in sheltered parts more or less thick black crusts appear. Although it is only 66 years old, it
shows the same corrosion effects as sculptures which are about 150 years or older.
Conservation plan
The basic conservation strategy for the Amazone has been similar to most of other bronze
monuments. It was decided to clean the surface from dirt and to put a microcrystalline wax (TeCero
3534F, Tromm Company) on it that might possibly be slightly pigmented in black to give an
impression of the original outlook.
The gilded and pigmented parts of the sculpture have been cleaned. This cleaning has been
performed mechanically due to the small amount of the gold layer.
After the cleaning also the coloured parts of the figure will be been coated with a microcrystalline
wax (not chosen yet). A wax having a slightly lower melting point than the TeCero 3534F will be
preferred. This and the sticking properties of the wax seem to be most suitable to consolidate the
fragile rests of the colouring and gilding.
There was a serious damage on the right arm of the Amazone, close to the shoulder: one of the big
iron screws which join the arm and the body of the Amazone was heavily corroded and had blown
out a covering bronze patch (Fig. 4..?). So the rest of the bronze patch and the iron screw has been
removed and cleaned and finally the patch has been replaced.
Fig. 4.?: Detail: damage at the right upper arm of the Amazone caused by an interior rusting iron screw. Credit:
Martin Mach.
There was a further damage on the right foreleg of the horse. Also in this case a small bronze patch
had been pressed out by the rusting armature.
Another problem is the joining of the sculpture with the base because until now it was only standing
loosely upon the base. In fact the sculpture had been moved some centimetres out of the centre of
the base. It might be knocked over its base by vandalists. As a consequence an appropriate join will
have to be constructed. The basic idea is to have a reversible joint. Under the plinth of the Amazone
are two unused bronze nuts with interior threads. Stainless steel rods will be fitted into these threads
and will be sticked into concentric cylindric tubes which will be fixed to the base. So it will be
possible to lift the Amazone from its base in a vertical direction but it will not be possible to knock
it from its base by a horizontal impact.
By Anke Doktor and Martin Mach
A Maintenance Plan
The damages on the monuments today are mainly caused by the bad environmental situation and a
lack of care. So obviously, apart from the improvement of the air quality, it is of great importance to
check the bronze monuments regularly.
But how can this be initiated? First of all there has to be financial support for any step of
maintaining an object. In most cases it is difficult to receive funds from the municipal authority.
Strangely it is easier to raise money for a big restoration that gets much public attention than to
support the maintenance with small amounts for a regular care.
After all the public has to become interested in the monument. It would be much easier if a kind of
association or organization could identify itself with the sculpture. A possibility could be for
example to sell the monument for a symbolic price of 1 Euro or simply give it as a present so that
the association is only responsible for the maintenance. It will surely find funds for an annual
cleaning and waxing. The aim should always be to make the public aware of the importance of the
maintenance of a monument. If this has been achieved, there may be a sponsor to be found who will
finance the restoration and of course be responsible for the care later on. These ideas are not very
new. In the late 19th century for example the foundry-men already appealed to the public to do a
cleaning of the sculptures every Saturday evening.
This is also the way that Sweden has developed in the last decades, selling out the property in
common to the market. But the disadvantages of this method are obvious, too. Sponsorship is soon
the only way for culture to exist. It may be a point to let associations be responsible - if they are
rich. Small associations will probably never pay for conservation.
Often an extensive restoration is most impressive for the public and the results are in most cases
very good. However conservation should not be restricted to these occasional and very expensive
measures. Regular care is just as important for a sculpture, otherwise after three years without care,
it will be in a bad condition again. Metal monuments are objects that need constant attention.
Therefore it is important for outdoor bronze sculptures to receive a regular annual service. After the
cleaning of the bronze surface with water and brushes usually a wax coating will be applied. This
kind of conservation has to be controlled and renewed every two years, at fountain sculptures even
every year. Therefore normally contracts with self-employed restorers are made.
A maintenance plan can also include yearly inspections, yearly cleaning with water, a control of all
measures performed concerning cultural objects and a documentation of all measures in a database.
The yearly inspection are occasions to check the overall state of the monument, the breakdown of
the coating on the bronze sculpture and how the patina or the corrosion layers are behaving. As a
result measures are taken to clean the non adherent deposits which may favour the corrosion
processes and to apply locally a new wax layer. Decisions about more important interventions
might be taken too and budgets planned.
Usually visits are conducted by professionals who are aware of corrosion processes on bronze
monuments. Their approach is then based on their experience. No monitoring technique tested until
now is performing well enough to assist them in their maintenance decision. It is then difficult to
tell exactly when and why some interventions are needed. It might happen that the corrosion that
has taken place is not so damaging for the monument (tarnishing) and the intervention is then based
only on aesthetic reasons.
If administrations have to be convinced to fund maintenance programs, they need to know why this
maintenance is needed and how much it will cost. In the following some original proposals are
made to give arguments to professionals to promote such maintenance programmes.
By Anke Doktor and Martin Mach
5.1 Athens experience
The city of Athens has not really any experience on maintenance programmes. When some damage
occurs on monuments (graffiti), an intervention is not always decided (except for Truman statue, as
I remember…).
Due to the interest of the City in the conservation of the Kolotronis monument, it has been decided
that a maintenance programme would be set up for this monument which could then be applied to
other monuments. As mentioned before, the study of the condition of the Kolotronis monument
revealed that the sculpture was not heavily corroded. The conservation treatment was then quite
basic and did not conduct to any dismantling and consolidation of the whole structure.
The maintenance of this monument does not seem to be an impossible task in that condition. But
the question is to know when the interventions will be needed. Monitoring techniques have then to
be developed. The team of professionals tried different tools for documenting and analysing the
condition state of the sculpture as it is now. Video films, X-fluorescence measurements at specific
areas and replicas of the surface were realised once the treatment was achieved and will be
compared to new results obtained in the future (when and how often?) to see how the sculpture
behaves with time.
Pictures are needed here.
Based on these data, it will be possible to propose a good maintenance programme and to budget it.
This approach will be then applied to other monuments in Athens exposed to a similar environment.
A survey of all the bronze monuments in Athens has first been conducted in parallel to the
programme and was based on the database established for this project. This survey has shown that
most of the monuments were suffering from graffiti applications. Otherwise they were in quite good
condition as it has been described previously.
A policy of cleaning of these graffiti as soon as possible will be needed before conducting a
conservation treatment.
By Vasilike Argyropoulos
5.2 Göteborg experience
Bronze monuments mean very much for the people who live in Göteborg and for the people who
visit the city. In the Municipality of Göteborg, where the Parks- and nature administration is caring
for the main part of the public art in the city, the consciousness have just awaken that outdoor art
will not last forever and that they will presumably last longer if they are cared for.
Until recently care for outdoor monuments have been neglected in Göteborg as well as in other
cities in Scandinavia. Maintenance has mainly been considered for functional damages, e.g. in
fountains, and sometimes for removal of graffiti and scrawl. Today, the only maintenance of
sculptures in Göteborg is cleaning after exposure to scrawl. The cleaning is done by building and
cleaning enterprises using methods that are not always the best for the monuments. Accordingly,
there is a lot to work for in this field.
The formulation of a conservation policy for outdoor art in Göteborg would be a great step in the
right direction. It could include how to regulate the antiquarian control for all measures concerning
cultural objects. It should also tell about how to take care of the monuments, and which
qualifications those who make the practical work ought to have, maybe some kind of certificate for
enterprises. Proper documentation of all the artworks and measures performed is necessary as well.
A database for the sculptures in Göteborg is now existing but need to be extended and updated.
These are all important issues to start with taking a step further in protecting our outdoor bronze
By Helen Svenstam and Helena Strandberg
5.3 Munich experience
The restoration and maintenance work performed by the Municipality of Munich and the Bavarian
State Department of Historical Monuments is based on a few assumptions that will be discussed
below. It has led to the following conclusions and practical hints with respect to maintenance.
5.3.a. The maintenance procedure and the basic philosophy behind
Every few years there are friendly suggestions by non-professionals interested in conservation to
analyse the preservation state of all monuments made out of metal scientifically and then to classify
them according to their degree of corrosion, soiling, graffitti and other criteria, all classifications
being based upon quantitative data only. Further on it is suggested to design a restoration and
maintenance plan which would foresee a clearly defined measure for each category. At the first
sight this might sound thoroughly reasonable and as a really logical and scientific way to proceed.
But when thought to the end it becomes obvious that such a procedure would in fact tend to
transform our monuments to homogeneous classes of uniform objects. Nobody would really want
that e.g. all wrought iron crosses of a cemetery would have exactly the same finish and the same
visual age appearance or that all bronze monuments would look just the same in spite of their
individual significance, their varying history and age.
It must furthermore be accepted as a part of our cultural diversity that some monuments tend to get
more attention and care by the public, whereas others might be rejected and that the interest in the
monuments as a whole will depend very much on the given economic and political situation.
Nevertheless probably all of us will agree that some basic care should be applied to all monuments,
so there will and should be a kind of typical restoration and maintenance procedure approach. This
approach as a rule will be not as rigid as the strict classification approach mentioned above but has
turned out as a good working solution in practice.
The philosophy behind maintenance is to avoid harsh cleaning and expensive restorations measures
by means a regular but mild cleaning and conservation procedure. This will at the same time
preserve the individual character of the monuments and broaden the intervals of restorations. All
bronze monuments therefore should be carefully cleaned on a yearly basis. Conservation coatings
should be checked and partially reapplied.
In case further steps like removal of crusts or new conservation measures should be considered as
necessary, care must be taken that this is in fact done by a professional restorer and that the
procedure will not be harmful to the monument or its patina layers. The term 'cleaning' tends to be
misinterpreted by untrained or not properly trained personnel. It has happened that the outer surface
of monuments was in fact completely destroyed by what was considered a 'cleaning procedure', e.g.
by sandblasting or acid treatment. Any kind of change in the maintenance procedure, above all the
use of new methods, should be discussed and decided by a group of conservation professionals.
5.3.b. Regular routine inspections - intervals and aims of the inspection
Though any type of appropriate surface conservation will persist for more than only one year,
a yearly inspection of each bronze monument is advisable. This inspection should also include a
look for possibly missing or deformed parts, for traces of rusty runoff indicating interior problems,
for graffitti and -which in fact happens rarely- newly formed cracks.
5.3.c. The financial and administrative basis
There must be a solid financial and administrative basis in order to implement and to carry on with
the maintenance procedure.
Of course there are many different styles in how to achieve and promote maintenance. As
maintenance is always a long-term issue it must be associated to long lasting administrational
structures, not to temporary projects. Nevertheless a project might help to attract private people's
and institutions' interests and can help to provide some funding.
There must be some kind of permanent active interest raising (public relations) and fund raising for
the monuments in order to guarantee mid-range and long-range maintenance. It might be also a
good practice to have restoration costs linked to subsequent maintenance costs, that means that an
institution that is willing to pay for a restoration should be asked to pay for subsequent maintenance
as well.
When looking back in history we will find nice examples of how long-term monuments' care was
planned already before 1900. There are examples of special foundations taking care for individual
monuments. It was also decided to have festivities around the monuments every year in order to
attract the public's attention to them and to have individual bank accounts for the regular inspection
and care of the monuments. As has been learnt in Germany even those wise precautions were soon
superseded by wars, economical crises, political changes and a lack of public interest.
As soon as the positive input ceases, controlling and cost cutting units within the administrations
and regional authorities will tend to cancel the respective funds in favour of other, seemingly more
urgent tasks. So the maintenance activities will always reflect the overall political and economical
situation and the number and power of individuals interested in the monuments. This also implies
that all of us can help in some way to contribute to perform a good job on the monuments or might
just remain lazy.
By Martin Mach
It is difficult to give a common approach for the management, conservation and maintenance of
outdoor bronze monuments from so different experiences. If the management and the conservation
are following strict rules in Munich, it is because the town has a long experience in the field and a
competent staff working everyday with professionals. In Göteborg, the professionals exist but the
administration has just realised how important it is to define specific methodology of management
and conservation for these monuments. In Athens, the subject is more or less completely new.
We have seen that the first step is the protection of the monuments. Once this work is done, the next
step is to have a team of professionals to deal with the specific problem of these monuments. This
team could include an art historian, a conservator, a scientist who would be in charge of the
documentation, the conservation and the maintenance of the monuments. If the states have to
initiate the project, the citizens interest in their monuments has to be restored. Publicity campaigns
are here needed.
Any conservation work cannot be done without considering the future maintenance of the
monument. Conservation strategies are globally the same all around Europe. What is different from
one country to another is the facilities and the staff dedicated to the conservation of these
monuments. Here rich western countries are favoured.
Maintenance guidelines exist in each country. Some are basic and are applied in all countries.
Others are most specific and depend on the particular interest of citizens or on tools developed with
the experience.
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The causes of deterioration of the gilded bronze doors of the Baptistery in Florence have been examined and the mechanism of corrosion discussed. An apparatus for thermal conditioning has been proposed and tested either on the north door of the Baptistery, or on samples exposed to the urban atmosphere in Milan and by laboratory tests on an electrochemical model. The effectiveness of the proposed apparatus has been verified by weight losses, by assessing soluble salts, by visual observations, by local chemical microanalyses, by morphological examinations with a scanning electron microscope equipped with an X-spectrometer and by X-ray diffraction.
An analysis has been completed of the state of degradation of the gilded surface of one of the 10 panels of the so-called ‘Door of Paradise’ of the Baptistry in Florence. This work, carried out by Lorenzo Ghiberti and completed by him in 1452, has, during the centuries, undergone a complex of chemical and physical phenomena which have profoundly altered the nature and appearance of the surface. Recently, with the advent of the industrial society, atmospheric pollution has produced changes which have accelerated in an alarming manner the degradation and loss of the already damaged gilding. The situation calls for an immediate cleaning operation, not only for aesthetic reasons but especially in order to remove from the surface all materials dangerous to the future conservation of this work of art. Three appropriate solvent-reagent systems have been selected and put to the test in the laboratory and in situ. Two of these consist of formulations of complexing agents: Rochelle salt and the trisodium salt of EDT A; the third is a mixed-bed ion-exchange resin. The experimental results fully confirm the efficacy and safety of the three substances.
A general review of some of the theories proposed to account for the process of "bronze disease" is presented from both the historical and chemical points of view. The corrosion product of most serious concern, cuprous chloride, and its inter-relationship with some of the other important corrosion products of copper alloys, such as the copper trihydroxychlorides, is reviewed. The critical RH for the transformation of cuprous chloride is discussed and suggestions are made concerning both the storage conditions for bronzes and the variety of conditions under which cuprous chloride can occur in excavated bronze.
Aged copper or bronze objects in outdoor environments exhibit patina layers containing several constituents. The influence of air pollutants on some of these compounds was studied, including cuprite (Cu2O), tenorite (CuO), brochantite (Cu4(OH)6SO4), antlerite, (Cu3(OH)4SO4), Cu2.5(OH)3SO4 · 2H2O, and a mixture of atacamite/clinoatacamite (Cu2(OH)3Cl). The compounds were exposed to air containing ppb-levels of SO2, O3 and NO2. The products were characterized by X-ray diffraction (XRD) after four weeks’ exposure. Deposition of SO2 and consumption of O3 were studied using on-line gas analysis. Mechanisms are suggested for the interaction of air pollutants with the patina compounds and the reactions are discussed in relation to outdoor conditions. The results are in agreement with observations from the field.Tenorite reacted rapidly with SO2 in humid air, acting as an ideal absorber. This observation is in agreement with the rare occurrence of this corrosion product in outdoor environment. In the case of cuprite, sulfates were produced in a humid SO2+O3 environment while no sulfate formed when SO2 was the only pollutant or when SO2 and NO2 were combined. However, active carbon on the cuprite surface enhanced the sulfation markedly in SO2+NO2 atmosphere. Cu2.5(OH)3SO4 · 2H2O, brochantite and antlerite formed on copper oxides. Cu2.5(OH)3SO4 · 2H2O, is suggested to be a metastable precursor in brochantite and antlerite formation and is slightly more soluble than these. Brochantite and antlerite did not react in any of the environments studied. In contrast, atacamite/clinoatacamite reacted rapidly with SO2 in humid air, forming soluble CuSO4 · xH2O and a CuCl2 · xH2O solution.
The influence of NaCl on patina compounds occurring on outdoor copper and bronze objects was investigated. The laboratory study included cuprite (Cu2O), tenorite (CuO), brochantite (Cu4(OH)6SO4), and antlerite (Cu3(OH)4SO4), pretreated with 10wt% NaCl. The pure compounds were exposed in humid air containing combinations of trace amounts of SO2, O3 and NO2. Phase transformations were characterized by X-ray diffraction (XRD) after four weeks’ exposure. Deposition of SO2 and consumption of O3 were studied using on-line gas analysis. Mechanisms are suggested and reactions are discussed in relation to outdoor conditions.Tenorite did not react with NaCl in humid air. However, when SO2 was added to the air, reaction was rapid, copper hydroxy chlorides and hydroxy sulfates forming. In addition, an unknown phase appeared in this environment. Cuprite pretreated with NaCl formed copper hydroxy chlorides in humid air. When SO2 was added to the air, the mixture absorbed all SO2 supplied. The rapid sulfation is suggested to be caused by the increased basicity due to oxidation of cuprite. Treating brochantite or antlerite with NaCl(aq) resulted in a remarkably fast conversion to copper hydroxy chlorides. The experiments demonstrate that copper hydroxy chlorides are expected to form on outdoor patina even in rain-exposed area. The lack of occurrence of hydroxy chlorides in these areas is suggested to be due to a progressing cyclic weathering; including the formation of hydroxy chlorides by salt deposition, the formation of soluble copper compounds by dry deposition of SO2, and subsequent wash-out by the rain.
Begleitet von einem umfassenden Meßprogramm für Umweltdaten wurden an 39 Stationen in 14 Ländern Kupfer- (DIN 1787) und Bronzeproben (DIN 1705) exponiert und anschließend untersucht. Gemessen wurden die Gewichtsveränderung, der Massenverlust (nach Abbeizen der Korrosionsschichten), die Farbveränderung (Dreibereichsverfahren), die chemische Zusammensetzung der Korrosionsprodukte (Debye-Scherrer), die Schichtdicke (Wirbelstromverfahren) sowie die Rauhigkeit der bewitterten Oberfläche (Perthometer). Die Korrosionsdaten stehen dabei im Zusammenhang mit den Umweltdaten, insbesondere der Schwefeldioxidkonzentration, der Leitfähigkeit der Niederschläge und der Luftfeuchtigkeit.The atmospheric corrosion of copper and bronze within the UN/ECE Exposure Programme. Intermediate report after 4 years of exposureAccompanied by an extensive measuring programme for environmental data, copper (DIN 1787) and bronze samples (DIN 1705) were exposed at 39 test sites in 14 countries and examined afterwards. Measured were the weight change, the mass loss (after pickling of the corrosion products), the colour changes (trichromatic colorimetry), the chemical composition of the corrosion products (Debye-Scherrer), the layer thickness (eddy-current method), and the roughness of the weathered surface (perthometer). The corrosion data are related with the environmental data, especially the concentration of sulfur dioxide, the relative humidity and the conductivity of precipitations.
The authors report on the reaction of SO[sub 2] and NO[sub 2] in sub-ppm concentrations in humid air with a copper surface. The deposition of SO[sub 2] was studied in a time-resolved manner and the formation of HNO[sub 2] was measured. Corrosion products were analyzed using XRD, FTIR, FTIRAS, and ion chromatography. S[sup IV]-O species on the copper surface was analyzed quantitatively using a sensitivity of 10[sup [minus]11] mol. Corrosion rates and corrosion products are reported. The corrosion of copper in humid SO[sub 2]-polluted air is accelerated strongly by the presence of NO[sub 2].