ArticlePDF Available

Recipes and experimentation? The transmission of glassmaking techniques in Medieval Iberia


Abstract and Figures

This paper explores the potential of a combined historical and archaeological approach to the study of glass production in the Iberian Peninsula in the Late Middle Ages. The historical study of technical recipes compiled during the Late Middle Ages and the Early Modern period and the compositional analysis of archaeological material offer different, but equally valuable, insights into glass production. The methodologies, potential and limitations of these techniques are summarised, and their combined use explored, with reference to a fifteenth-century letter written by one Cristóforo de Soto Mayor, its experimental reconstruction, and the comparison of these results with real archaeological datasets.
Content may be subject to copyright.
Full Terms & Conditions of access and use can be found at
Download by: [University of Leicester] Date: 02 September 2016, At: 05:24
Journal of Medieval Iberian Studies
ISSN: 1754-6559 (Print) 1754-6567 (Online) Journal homepage:
Recipes and experimentation? The transmission of
glassmaking techniques in Medieval Iberia
David J. Govantes-Edwards, Chloë N. Duckworth & Ricardo Córdoba
To cite this article: David J. Govantes-Edwards, Chloë N. Duckworth & Ricardo Córdoba (2016):
Recipes and experimentation? The transmission of glassmaking techniques in Medieval Iberia,
Journal of Medieval Iberian Studies, DOI: 10.1080/17546559.2016.1209779
To link to this article:
Published online: 02 Sep 2016.
Submit your article to this journal
View related articles
View Crossmark data
Recipes and experimentation? The transmission of
glassmaking techniques in Medieval Iberia
David J. Govantes-Edwards
, Chloë N. Duckworth
and Ricardo Córdoba
Facultad de Filosofía, Universidad Nacional de Educación a Distancia, Madrid, Spain;
School of Archaeology
and Ancient History, University of Leicester, Leicester, UK;
Departamento de Ciencias de la Antigüedad y la
Edad Media, Universidad de Córdoba, Córdoba, Spain
This paper explores the potential of a combined historical and
archaeological approach to the study of glass production in the
Iberian Peninsula in the Late Middle Ages. The historical study of
technical recipes compiled during the Late Middle Ages and the
Early Modern period and the compositional analysis of
archaeological material offer different, but equally valuable,
insights into glass production. The methodologies, potential and
limitations of these techniques are summarised, and their
combined use explored, with reference to a fteenth-century
letter written by one Cristóforo de Soto Mayor, its experimental
reconstruction, and the comparison of these results with real
archaeological datasets.
Received 29 February 2016
Accepted 3 July 2016
Glassmaking; technical
recipes; archaeometry;
Iberian Peninsula
The study of technology is a recurrent topic for both historians and archaeologists, and
recent decades have witnessed a considerable increase in the theoretical and methodologi-
cal complexity with which the issue is approached. Within this general context, glass pro-
duction has received much attention, but the Iberian Peninsula remains somewhat behind
other regions in the Mediterranean world in this regard.
That special attention is paid to
glass production in the Eastern Mediterranean and the Near East during the second mil-
lennium BC, the region and period in which glass was invented, seems to make sense, but
the perpetuation of this research bias for other periods (for example, the Late Middle Ages)
in which glass was pretty much universally known, circulated and produced is question-
able. At any rate, as we shall see in more detail below, the study of glass production in the
Iberian Peninsula in the Middle Ages is still in its infancy, especially concerning the tech-
nological aspect.
This state of affairs is a little perplexing, since the Iberian Peninsula stands as a unique
example of direct, and often peaceful contact between two very different cultural horizons:
Western Christianity and Islam. That the direct transfer of complex technological pro-
cesses occurred between al-Andalus and the Christian kingdoms to the north is a well-
known fact, for example with ceramic lustrewares; originally developed in the Nasrid
© 2016 Informa UK Limited, trading as Taylor & Francis Group
CONTACT David J. Govantes-Edwards
Duckworth et al., El vidrio andalusí.
kingdom, the production of Malaga lustrewareswas eventually adopted in Christian
There is, however, still a lot to be unpicked in this regard. Technological inter-
action in a particular eld is hardly ever a one-off event involving the wholesale adoption
of a certain practice; rather, it is a much more complex process full of twists, counter-twists
and individual acts of adaptation, invention and rejection, especially when such different
approaches to production, identity, power and religion as Islam and the medieval Chris-
tian West are involved (and this is without even mentioning the presence of a very signi-
cant third factor in the equation: the Jewish contribution to the history of Medieval Iberia).
In order to contribute towards solving this historiographical anomaly, we propose to
examine the potential of combining two very specic strands of evidence chemical com-
position and technical recipes as means of determining the technological practices
involved in glass production. As we shall see in detail below, compositional evidence
for glass from the Islamic period/areas is becoming increasingly available, but the infor-
mation provided by Arabic written sources is close to non-existent. Conversely, the
written record for the Christian period/areas is much richer, including some highly
detailed documents, but the compositional evidence is limited, to our knowledge, to
church window glass (addressed below). The really interesting thing here is that, as far
as glass production is concerned (as well as for so much else), what we have just called
Islamic and Christian period/areasare conventions; the reality was much more uid
and frontiers much more permeable. This we already know on the basis of a few signicant
pieces of evidence. Firstly, we know that after the end of the Christian conquest of
Granada, in 1492, a type of Islamic glass known as Castril continued in some areas of
the former Nasrid kingdom until the seventeenth century and even later.
Secondly and
crucially, the use of plant ashes in glassmaking may have been introduced to the
Iberian Peninsula by the Muslims, but seems to have been adopted at a relatively early
stage in the Christian territories, as shown by Thomas Glick.
The methodologies involved in the study of these different strands of evidence are, as
may be imagined, nothing alike, but they make good partners, as we hope to demonstrate,
yielding a result which can be much more than the sum of its parts. As well as allowing
both the historian and the archaeologist to take their conclusions much further, they
open an interesting path towards more general, and probably also more fruitful, elds
of enquiry, such as the perspective on technological practice and exchange as a social
feature of different, but interlocking, human groups.
A (very) brief introduction to glass in history
The earliest glassmaking industry developed in the mid-second millennium BC in Meso-
potamia, and spread from there to Egypt and the eastern Mediterranean. Written
responses to the new material reect an interest in its properties, particularly that of
Colour was understood as a key, inherent material property, and the ability of
García Porras, El azul en la producción,267.
Frothingham, Spanish Glass,529.
In 1189 the monastery of Poblet granted to the glassblower Guillem the right to gather glasswort in return for tithe and
two hundred pounds of sheet glass paid annually.Glick, Islamic and Christian Spain, 241.
The earliest known recipes thought to pertain to glass are strongly framed around the creation of various colours. See
Oppenheim et al., Glass and Glassmaking.
glass to fully assume a whole range of different colours may well have been a factor in its
high value at this early stage.
The production of a particular colour of glass, or the elim-
ination of colour from glass, remains a signicant theme in the corpus of early glass recipes
known to us.
Why the focus on colour? We can suggest several explanations for this. In its earliest
iteration, glass was seen as a form of precious stone: its colour and potential for poly-
chromy were central to its value. In the Roman period, following the invention of glass-
blowing, the material became quotidian for the rst time in its history, and was now
able to take on practicalfunctions, for example its use in storage and transport contain-
ers, as a drinking vessel (which, unlike metal, did not add its own taste to the contents),
and in lighting. In these contexts, the key factor was not the colour of the glass, but its
translucency. From a textual perspective, it is likely that much of our knowledge of
Roman glassmaking is a response to the relatively rapid expansion in the use of glass as
a material, including its mass production and recycling. A fair proportion of the texts
describing glass production date from the rst century AD, around the time that this
expansion took place.
At the same time, the production of luxury glass continued, and
the expense of this glassware was often highlighted in the choice of colourants employed
and the use of time-consuming production techniques: the classic example combining
both is the famous fourth-century Lycurgus Cup.
Nonetheless, and perhaps because of
the importance of translucency in this period, we have few references in the Roman
period to colouring glass. By the medieval period, with the expansion of the use of
window glass and enamelled decoration, polychromy in glass is again a subject of detailed
consideration, and texts such as the so-called Bologna Manuscript, written in the fteenth
include expositions of the different mechanisms by which glass can be coloured.
An early example of a new direction for glassmaking texts is provided by the twelfth-
century book on glassmaking by Theophilus Presbyter, who has been identied with
Roger of Helmarshausen: in addition to a description of the production of different
colours of glass by varying the redox atmosphere
in the furnace and by recycling
Roman glasses, it focuses in detail on furnace construction and the production of
certain types of glass object (windows, asks, rings).
The description of furnaces was
later followed in such treatises as AgricolasDe re metallica and Vannoccio Biringuccios
Pirotechnia (both sixteenth century in date).
Interestingly, the latter text includes a long
consideration of the beauty of different colours of glass, but offers no insights into how
these are produced.
Duckworth, Imitation, articiality and creation.
See for example: Pliny, Natural History 36.106, 109, 110, 1909, 37.29; Josephus, Jewish War 2.18990; Strabo, Geography
16.2.25; Martial, Epigrams 1.41.15, 12.74, 94; Statius Silvae 1.6.704.
Freestone et al., The Lycurgus Cup.
Merrield, Original Treatises. The treatise was found in the nineteenth century in the convent of San Salvatore, in Bologna,
but the authors do not know its current whereabouts.
In simple terms, the redox conditions refer to the potential of the atmosphere for either reduction (loss of electrons) or
oxidation (gain of electrons) of the materials being heated. In practical terms, redox atmospheres are varied by altering
the amount of oxygen and carbon, so that a highly oxidising atmosphere is one with an excess of O
, whereas a highly
reducing atmosphere has an excess of CO (carbon monoxide).
Theophilus Presbyter, On Divers Arts,4774.
Agricola, De re metallica; Biringuccio, Pirotechnia.
A (very) brief introduction to the chemistry of glass
Before we proceed any further it may be a good idea to make a very brief introduction to
the chemistry of glass, so the reader can follow the arguments below. The three main com-
ponents are a glass former, chiey silica (SiO
), an alkali ux, mostly soda (Na
O) or
potash (K
O), and a stabiliser, namely lime (CaO). The silica, which is the principal struc-
tural component of the glass, can be extracted from sand or from crushed quartz pebbles,
which are a particularly pure source of silica. The alkalis (soda and potash), for their part,
act as uxes, lowering the melting and working temperatures, and can be extracted from
mineral sources, for example natron, or from vegetal sources, such as halophytic plant
ashes for soda and other vegetal ashes (e.g. beech wood) for potash. Finally, the lime,
which stabilises the structure and prevents its dissolution in water, can be extracted
from different sources such as shell (often present in the glassmaking sand), limestone,
bone, or the same plant or tree ashes used as a source of alkali. Glasses are typically pro-
duced at temperatures in excess of 1100°C, though temperature varies along with time of
heating, composition of glass, and the grain size of the raw ingredients.
Most ingredients are added to the mix in the form of carbonates, but the carbon burns
off during production, leaving the glass as a network of oxides. It can be seen that some
combinations of raw ingredients (e.g. beach sand + plant ash) will provide all three necess-
ary ingredients (former, alkali, stabiliser), whereas others (e.g. quartz pebbles + mineral
soda) will not, and the glass will either fail, or will be unstable and may not survive in
the material record. Impurities can have negative consequences on colour and working
properties, so another factor relevant to glassmakers would be the combination of raw
ingredients in such a way as to minimise impurities.
Technical recipes in the context of medieval glass making in the Iberian
Technical recipes are a sui generis source of historical information. These texts describe the
steps taken in different technical processes and indicate the various raw materials and
equipment that need to be used to obtain a certain product. However, the category tech-
nical recipeis a construction in a very Latourian way; the category is rather broad and
exible, and can include a wide variety of texts written for very different purposes and
for very different audiences. We cannot approach St. Isidore of SevillesEtymologies,a
seventh-century encyclopaedic compilation of general knowledge which includes some
technical references to glass,
in the same way in which we read TheophilussOn
Divers Arts, a twelfth-century specialised technical treatise on painting, glassmaking and
and aimed at the craftsman, Hieronymus MünzersItinerarium Hispanicum,
a geographical description of late fteenth-century Spain in which, again, some technical
references to glassmaking are made in passim,
or, a commercial agreement in which
transactions involving the raw materials used in glass production are detailed.
general, all historical sources must be considered critically, that is, taking into account
Isidore of Seville, The Etymologies, 328.
Theophilus, On Divers Arts.
Pfandl, Itinerarium Hispanicum.
Glick, Islamic and Christian Spain, 241. Otte, Sevilla y sus mercaderes, 88-9.
their original aim, their transmission, and any other factor that may affect their value and
scope as historical evidence,
but this is especially relevant when dealing with a con-
structed textual category, such as technical recipes.
Even when recipes are part of a technical treatise written or compiled by someone who
understood the technologies being recorded, we should not assume that they will be com-
plete and systematic, as anyone who has studied them in detail knows. These recipes can
be surprisingly erratic and vague for a kind of text which, from our own perspective,
should be the epitome of orderliness and completeness. The reasons for this are multiple.
The most obvious is perhaps the possibility of copyists and compilers making mistakes,
which is especially plausible when said copyists and compilers had no knowledge of the
technical procedures described in the text.
However, the incompleteness could very well be intentional, which is not to say delib-
erately misleading (at least not always). If we send a colleague an email explaining how to
operate a new piece of software, we do not open our email with the instruction: turn the
computer on; that much is assumed. If a recipe was put down in writing by an expert
craftsman and addressed to a peer, the standard procedures would be likewise assumed
and not committed to writing for being obvious to them, if not to the non-expert. On
the other hand, we must remember that information is not a free item, and that technical
knowledge is sometimes guarded jealously. History is full of examples of crafts that were
kept secret, sometimes for long periods of time, for their value as instruments of power, the
most obvious being, perhaps, writing itself.
A splendid example of this is provided by the
potters of Muel (Zaragoza, Spain), who in the late sixteenth century gave to Henrique
Cock, a member of Philip IIs retinue, the instructions for making lustre-wares, which
include the use of un poco de alambre, that is, a little copper.
What is unclear
from the manuscript (but becomes clear upon scientic investigation) is that copper is
the key in this procedure, and unless it is added in exactly the right amount, the instruc-
tions are simply worthless. In effect, the potters from Muel possibly quite deliberately
told Henrique Cock nothing of any use.
A key factor to consider here, therefore, is the
purpose behind putting the recipe down in writing in the rst place. Let us assume, for the
moment, the idea that the glassmaking texts under discussion were written with the
purpose of allowing a craftsperson to follow and reproduce the recipe. We would argue
that, in spite of all the care taken to include relevant details such as weights and types
of raw material, it is all but impossible to translate the act of making glass into a text in
such a way that it could be followed from scratch. For example, experimental archaeol-
ogy and ethnography tell us about the central importance of furnace design to the success
of a glass production recipe. The temperatures involved in glass production are extremely
high, and different temperatures are required for different processes, so furnace design,
fuel type and temperature control are vital factors in success. Yet prior to the sixteenth
century, few recipes even mention the type of furnace to be used. The texts, clearly,
were not designed with the aim of describing the entire chaîne opératoire of glass pro-
duction. Prior knowledge is required: recipes and other texts are aimed at augmenting,
Martinón-Torres, Why Should Archaeologists, 26; Córdoba, Un recetario técnico,8.
Martinón-Torres, Why Should Archaeologists, 27; Smith and Hawthorne, Mappae Clavicula, 15.
Goody, The Logic of Writing.
Morel-Fatio and Rodríguez, Viaje de Felipe II, 31.
Pérez-Arantegui and Pardos, Lustre recipes, 164.
and perhaps adjusting this. Indeed, there is a great difference between the sort of knowl-
edge which can be transmitted via text, and the sort of knowledge which must be acquired
through praxis. There are also social hierarchical associations with different types of
knowledge, and those with the knowledge of controlling a furnace atmosphere which
is dirty, and learnt by praxis would almost always have lower status than those with
the knowledge of, for example, which minerals to use to create a desired colouring effect.
Another factor which was signicant in the production of many past glassmaking
recipes is their role as elements of alchemical treatises.
The aims of such texts vary,
but one theme which recurs throughout the history of glass production is that of
control over the natural world. Recipes were not necessarily designed to transmit knowl-
edge as much as to demonstrate the possession of that knowledge by the owner of the com-
pendium, and the library in which it was housed. Alchemy itself is the ultimate quest for
control over the natural world, and the changing of a materials inherent qualities was a
signicant step in this.
Turning to the specic matter of glassmaking in the Iberian Peninsula during the
Middle Ages, what recipes do we have? The answer, unfortunately, is not many (see
Table 1). Perhaps it is best to begin by mentioning two alchemical compendia, Alfonso
XsLapidario, compiled in the thirteenth century, and a work known as Sedacina, com-
piled by a Guillaume Sedacer in Catalonia in the late fourteenth century. In these compen-
dia, glass is presented by virtue of its alchemical properties; the value of these texts as a
source for the history of technology is thus limited.
The prologue of the Lapidario spur-
iously claims that at least some of the recipes are based on Aristotle, via the transmission of
Arabic scholars (specically, the mysterious Abolays),
but it must be kept in mind that
this work was being compiled during the apogee of the so-called School of Translators of
Toledo, which was in the process of translating most of Aristotles works into Latin from
Arabic, and which was to have a deep and lasting effect on Western science and philos-
In any case, the attribution of work to earlier, even mythological personages is
a recognised difculty in alchemical texts.
A completely different kind of text is manuscript H-490 from lÉcole de Médicine of
Montpellier University, written sometime between 1460 and 1480, which includes one
recipe on how to prepare glazing and three on how to colour glass. It is a nice example
of some of the typical features and problems of technical recipes during this period.
First it is a miscellaneous compilation of texts, most of which deal with medical and bota-
nical issues.
Moreover, only recipe number 31 gives a very schematic account on how to
prepare glass from scratch while the others simply seem to assume that whoever is inter-
ested in dyeing glass red or green does not need telling how to make glass in the rst place.
Concerning transmission, recipe number 33 in manuscript H-490 is, according to the text,
based on Albertus Magnus, Thomas Aquinass tutor and famous in the Middle Ages for
the scope of his scientic curiosity (and his Aristotelian leanings!). We have not had
the opportunity of examining Albertuss vast bibliography in full, but sufce it to say
Barthélemy, La Sedacina ou loeuvre au crible; Neri, The Art of Glass.
Rodriguez, Lapidario; Barthélemy, La Sedacina ou loeuvre au crible.
Amasuno, En torno a las fuentes.
Martínez Lorca, Maestros de occidente.
Hill, Arabic alchemy.
Córdoba, Un recetario técnico,9.
that this glass recipe is not to be found in Of the Virtues of Herbs, Stones and Certain
Beasts,The Book of Minerals or On the Causes of the Properties of the Elements,
are the three works by Albertus Magnus in which this sort of information is likely to be
expected. This means that either the attribution of the recipe to Albertus Magnus is spur-
ious or that the recipe is in one of Albertuss works which are not explicitly concerned with
the natural sciences or the properties of materials. As we can see, the routes of medieval
transmission can be circuitous indeed, which does not always make for a straightforward
historical record.
We also have the document known as Epistola Abbreviatoria, a letter dated to the late
fteenth or the early sixteenth century, in which a Christóforo de Soto Mayor addresses his
friend Juan de Alcalá and gives him the recipe to produce three qualities of glass.
there is the German geographer Hieronymus Münzers (also spelled Müntzer) account of
his travels through the Iberian Peninsula in 14941495. Interestingly, apart from a very
schematic description of the technique to make glass (which betrays his knowledge of
Table 1. Summary of texts related to glassmaking in the Iberian Peninsula.
Author and
common name of
Type of text and
language Date
Location(s) to which
the text pertains
Provenance of technical
Don Christóforo of
Soto Mayor,
Letter, Latin Early sixteenth
Galician writing to
friend in Alcalá.
Refers also to Bishop
of Córdoba.
Refers to how glass used to
be made (Lat. Olim). Source
(s) unknown.
Guillaume Sedacer,
Alchemical treatise,
1378 and
Sedacer was
Catalonian, and
spent time in
Catalonia and
southern France.
Other medieval treatises, e.g.
TheophilussDe diversis
artibus. Cites lists of sources
in the Arabic tradition. Links
to alchemical conclusions
Alfonso X (El Sabio),
Astrological and
treatise, translated
to Castellano
original c.1250,
Castile (Alfonso X) Prologue claims that the text
originates in the writings of
Aristotle. Probably owes
much to Arabic Lapidaries.
Juan Celaya (?)
Compilation of texts,
mostly medical and
146080 The only recipe which makes
reference to origin of
information refers it back to
Albertus Magnus, but this
has not been conrmed.
14945 Description of
glassmaking in
Murcia by German
humanist from
Isidore of Seville,
The section on glass
production is based upon
PlinysNatural History, which
refers specically to the
production of glass in the
Iberian Peninsula, though
this is not .
Pedro Gil, Historia
natural de
c. 1600 Catalonia
Best and Brightman, The Book of Secrets; Wyckoff, Albertus Magnus; Albert the Great. On the Causes.
Whitehouse, The Epistola Abbreviatoria, 3557.
the plant ashes used for this purpose in Germany), Münzer also described the abundance
of a plant called kali,sosam or zozam in the vicinity of Alhama de Murcia, a glassmaking
In conclusion, we are currently aware of just a few recipes (see Table 1 for summary);
and more signicantly, we have none from the Islamic regions of Iberia. This is in conso-
nance with a general paucity of written records concerning the production of glass in al-
Andalus. The only direct reference we know of is by al-Maqqari, a seventeenth-century
historian, who quotes Ibn Said (thirteenth century), who mentions the excellence of
glass productions from Almeria, Murcia and Malaga, and makes one passing reference
to the use of stonesto make glass.
That no Andalusi accounts of glassmaking have
reached us is indeed unfortunate, for glass technology in other Islamic regions was
described in some detail, for example by al-Jabir (eighthninth centuries), Almassoudi
(ninthtenth centuries) and al-Biruni (tentheleventh centuries).
Methodology: compositional analysis
A variety of analytical techniques exist with which the chemical composition of glass may
be measured. Most of these rely upon generating and ring high-energy waves or particles
(e.g. electrons, X-rays) at the sample, and measuring one or more of the resultant emis-
sions (by mass, wavelength, or energy). These results are compared with a suite of stan-
dards of known composition, and used to determine the chemical make-up of the
sample. In addition to techniques designed to characterise the bulk chemical composition
of a material, it is possible to measure various isotope markers of the geological origin of
the raw ingredients, which can be very useful in the denition of the provenance of specic
ingredients, such as lead or sand.
These techniques are able to offer insight into the technologies involved in the pro-
duction of a glass item. However, there are also important limitations to compositional
analysis, which have essentially to do with the nuances of the archaeological material
on which they depend, and of which we shall only mention the most common. To
begin with, glass is fragile, and it does not always survive in recognizable conditions in
the archaeological record, so the amount of evidence available for sampling and analysis
is limited. Moreover, all archaeological materials, including glass, are subject to deposi-
tional and post-depositional processes which can affect their reliability as evidence; only
items found in well-excavated and closedarchaeological contexts should be used for
analysis, as decontextualised analytical results are of little value. In addition, in the past
as today, goods could move about quite a bit, for example through trade, and nothing
guarantees that a piece found in a particular geographical and chronological context is
representative of technological practice in said context. In this regard, context is vital,
and all analytical programmes should consider as large as possible a population of
samples to ensure maximum representativeness; however, due to sampling issues and
analytical costs the ideal is rarely achievable. To make contextualisation even harder,
Pfandl, Itinerarium Hispanicum,345.
Jiménez, El vidrio andalusí, 117; de Gayangos, Mohammedan Dynasties, 148 (Vol I); 311 (Vol II).
Henderson, Ancient Glass, 2635; Young and Latham, Religion, Learning and Science, 32841, 40523.
For detailed coverage of the most common analytical techniques available to archaeologists, see Pollard and Heron,
Archaeological Chemistry.
glass production facilities are very elusive; most known examples in Spain were located in
urban and suburban areas, and their archaeological exploration more often than not
depends on urban rescue archaeology, which takes place in a context of nancial
and time pressure, and thus rarely provides the most adequate tools for specialised
research. This means that items found in non-production contexts (e.g. consumption,
domestic, religious) are seldom open to direct comparison to production remains from
the same period and region. Finally, glass is not only recyclable, but we know that it
was recycled on a vast scale in the past. A good illustration for this is the eleventh-
century Serçe Limani shipwreck, the remains of a westbound ship found off the
Turkish coast. This ship was loaded with a cargo of glass intended for further working
which, signicantly, included not only chunks of rawglass, but also glass cullet, that
is, broken glass items, presumably to be re-melted and re-shaped at the cargos destina-
Recycling has the effect of muddying the outcome of compositional analysis,
for example by offering results that appear somewhere between the ranges of known com-
positional groups.
In Spain, little has been done concerning the compositional analysis of medieval glass.
The only quantitative studies published to date that concern Andalusi glass are, to our
knowledge, a batch of material from the excavation of an eleventh- to twelfth-century
glass workshop in Murcia and a group of samples from different domestic contexts
in Córdoba, between the ninth and the twelfth centuries.
Another group of
samples, in this case from Malaga (twelfthfourteenth centuries), has also been
analysed by the authors of this paper and others, but is awaiting publication. In addition
to this, the other eld in which analytical work has been carried out concerns church
window glass.
The reconstruction of a glassmaking recipe: Don ChristóforosEpistola
In order to make an in-depth exploration of the way in which we can combine the evi-
dence of a written recipe with that of archaeological and archaeometric analyses, we
focused on the text written by Don Christóforo. This incomplete text, summarised by
David Whitehouse,
was written by one Don Christóforo of Soto Mayor (Galicia) to
his friend, Juan of Alcalá, around the rst quarter of the sixteenth century.
It is
unclear which AlcaláJuan was from there are a good few in Spain but we believe
its contents to be of potential relevance to southern Spain (and thus the lands which
were under Muslim rule for the longest) as Christóforo mentions that he has made
requests to the bishop of Córdoba for books about glassmaking.
A further signicant fact about the letter is that Christóforo claims he is describing tra-
ditional, rather than contemporary, glassmaking. This naturally raises some questions
about the origin of his information: was it copied, or based on personal observation?
Bass et al., Serçe Limani,4.
Carmona et al., Islamic glasses, 43945; Duckworth et al., Electron Microprobe Analysis,2750.
Window glass is a specialism in itself, and going into details about these compositional studies is well beyond the scope of
this paper. For results and discussion, see Bazzochi, Las vidrieras góticas; Carmona et al., Vidrios y grisallas; Alonso et al.,
Un vidrio medieval.
Whitehouse, The Epistola Abbreviatoria.
On dating the text, see Whitehouse, The Epistola Abbreviatoria, 355.
The part of the letter which is of the most relevance to us is that which reports on the
making of raw glass. Three different qualities are described: inma (the lowest quality),
christallina (middling quality) and physica (the best quality).
The key stages in the recipe for inma glass are as follows:
1. Take three parts of sosa or salicornia (which glassmakers call barrilla).
2. Pound one part of sand or nely ground pebbles.
3. Mix them, add ordinary water and form the mixture into loaves.
4. Dry these in the furnace and cool them.
5. Melt them in pots, leaving them for at least one night, or [preferably] 24 hours.
6. With an iron spoon, continuously remove the scum that rises to the surface and is
known in the vernacular as anitron salt.
7. You will know that the glass is ready when it adheres to the tip of an iron rod and
remains clear.
8. Then for every 100 pounds of the melt, add one ounce of manganese (which glass-
makers call tinta spiritorum).
9. Mix it well and immediately the melt will become violet wait until the colour settles to
the bottom, and you have white [colourless] glass ready to receive any other colouring
The recipe for the christallina glass is similar, but uses two parts of clear, white ground
quartz pebbles rather than one part of sand, and only uses the sosa plants. The physica
glass has a different ratio again: one to one of sosa plant ashes to ground pebbles.
Making the glass
We followed the recipe for inma glass, using modern washed silica sand and the ashes of
halophytic plants from locations in Almería and Murcia. Table 2 summarises the ingredients.
The plants were mainly gathered from sites in Murcia, although some plants from
Almería were also included. The majority of the ashes came from Alhama de Murcia,
which was famous as a centre of glassmaking, and was also mentioned by Münzer in
the Itinerarium Hispanicum, as noted above. Samples of the gathered plants were dried
and ashed at 650°C. No further treatment was applied, save for that suggested by Chris-
tóforo himself and outlined below.
The experiment was conducted using a modern electric furnace, made by Vecstar Ltd.
and housed in the School of Archaeology and Ancient History, University of Leicester. The
furnace has a maximum temperature of 1300°C and can be programmed to raise tempera-
ture incrementally. The glass was red in this furnace to 1150°C under an oxidising atmos-
phere, according to the temperature chart shown in Figure 1.
Because our experimental setup did not allow us to stir the glass during production, we
were unable to follow this part of the recipe. In fact, the outcome demonstrates that it is
probably a crucial part, as we were left with just a small fraction of glass beneath a mass of
bubbly, frit-like material, opaque white in colour (Figure 2). Frit is the term for a sintered
The term barrilla is a generic name used to refer to a group of plants rich in sodium, the ashes of which were profusely
used in glassmaking. The term originates in the Iberian Peninsula but became widely recognised throughout Europe due
to the good reputation of barilla ashes from at least the seventeenth century.
(semi-fused) fusion of the glassmaking ingredients, and in some glass production oper-
ations it is a key initial stage in glassmaking, with the frit being crushed and reheated
to form true glass.
Initially, we suspected that the frit-like formation was a scum resulting from the indis-
criminate use of untreated plant ashes: if plant ashes high in sodium chloride (NaCl) as
well as those rich in sodium carbonate (NaCaO
) were employed, we could expect the
chlorides to form an immiscible scum on the surface, as the solubility of chlorine in
glass is highly limited.
Another possibility, however, is that the glass simply had insuf-
cient reaction time: it was not held at temperature for very long, and as Don Christóforo
offers little information on the operation of the furnaces, we cannot be certain that either
our maximum temperature or soak time was an accurate reconstruction of those used in
the fteenth and sixteenth centuries.
Samples of the frit-like material formed by the experiments and the small amount of
successful glass produced were analysed using a Horiba XGT-7000 micro X-ray uor-
escence spectrometer (School of Archaeology and Ancient History, University of Leice-
ster). The sample was analysed under full vacuum, with an acquisition time of 300
seconds, 15 kV accelerating voltage and 1 mA current, and beam diameters of 100 µm
and 1.2 mm. The points selected for analysis are shown in Figure 3.
Table 2. plants used for the experiment. Plants from several locations were combined due to limited
availability (the plants were originally gathered by us for quantitative analysis, which is yet to take
place). The species identications are tentative only, as we have not yet consulted a botanist.
Weight of dried plants Gathered at (location) Geographical coordinates of sample Species
10.8 g San Pedro de Pinatar, Murcia 37°4935.22′′N
Sarcoconia perennis
75.4 g Alhama de Murcia, Murcia 37°4634.34N
Halogeton sativus
19.6 g San Pedro de Pinatar, Murcia 37°4938.45′′N
Sarcoconia perennis
21.2 g Cabo de Gata, Almería 36°4426.38′′N
Salicornia europaea
8.8 g San Pedro de Pinatar, Murcia 37°4935.22′′N
Salicornia europaea
Figure 1. Time-temperature chart for the ring. The glass was held at a temperature of between 1146°
C and 1152°C for an hour, before being allowed to cool within the furnace.
See for example Tanimoto and Rehren, Interactions between silicate and salt melts, 2567.
The results of µ-XRF analysis are semi-quantitative only. The results for the most con-
sistent glassy phase analysed are reported in Table 3.
Figure 2. (a) Halophytic plants prior to ashing; (b) the sand; (c) plants after ashing; (d) loafof plant
ashes, sand and water; (e,f) the loaf after ring; (g,h) the vitreous product after the second ring.
Silicon, as to be expected, is the most abundant element detected. It derives from the
sand and is the glass former. Also likely to have come from the sand are aluminium
and iron, and possibly the small amount of titanium and the trace of manganese. Probably,
the rest of the identied elements largely, if not entirely, derived from the plant ashes.
These include the alkalis (sodium and potassium) and calcium (a crucial ingredient in
soda-silica glasses as it acts as a stabiliser), demonstrating that the plants ashed were suit-
able choices for glass production insofar as they contained the two necessary ingredients
not found in the sand (alkali and lime, CaO). Interestingly, the results for all areas analysed
included a signicant proportion of chlorine, apparently close to its limit of solubility in
soda-silica glasses, though the poor accuracy and precision of the analytical technique
means that we should interpret all reported results as broadly as possible.
Discussion: Don Christóforos text and glass production in al-Andalus
In order to investigate whether the combined use of a glassmaking recipe with archaeolo-
gical and archaeometric approaches can shed any light on the earlier glass production
industry of al-Andalus, we now offer some comparisons between the results presented
Figure 3. Close-up image of the analysed cross-section (left) showing the presence of glassy phases
within the crystalline mass of the red batch, and the three points (marked with an x) selected for
Table 3. Elements, with mass percentages normalised to 100 by the XRF software. Results are rounded
to whole numbers for any reading >1 wt%, and listed as tracefor any reading <1 wt%. Note that in
reality the elements, with the exception of chlorine, are bonded in the glass with oxygen.
Element Read mass % (normalised to 100) Probable raw ingredient source
Na (sodium) 14 Plant ashes
Mg (magnesium) 5 Plant ashes
Al (aluminium) 2 Sand
Si (silicon) 66 Sand
P (phosphorus) trace Plant ashes
S (sulphur) trace Plant ashes
Cl (chlorine) 2 Plant ashes
K (potassium) 3 Plant ashes
Ca (calcium) 7 Plant ashes
Ti (titanium) trace Sand
Mn (manganese) trace Sand, plant ashes
Fe (iron) trace Sand
above, the information provided in the text itself, and the rst results of our compositional
research into medieval glass in Cordoba and Malaga.
Despite using orange-coloured sand for our experiments rather than the purest white
quartz pebbles suggested for the higher qualities of glass, the small fragments of glass
which we produced were clear and colourless in appearance, while the crystalline, frit-
like material which formed the majority of the product was white in appearance. This indi-
cates that the plant ashes were relatively free of the sorts of impurities which produce
unwanted colouring effects in the glass.
We might thus assume that the need to decolourise the glass with manganese, as
described in Christóforos description, arose from the use of a relatively impure sand
source. An alternative explanation is that the repeated use of an iron spoon at high temp-
erature, in order to remove the scum from the surface of the glass melt, would have intro-
duced a signicant iron impurity to the glass. The two explanations are not mutually
exclusive, and both sand and tools are potential contributors of iron to glass. The fact
that even glasses made from the purest silica sources described by Don Cristóforo were
subjected to decolouring may support this view.
In this vein, it is interesting to note that relatively high iron was a feature of ninth- to
twelfth-century Islamic glasses from Cordoba.
Initially this may seem to support the idea
of contamination, but the iron in these glasses was strongly correlated with alumina (R
0.89), suggesting a common source for the two. The most likely source of both iron and
alumina is the glassmaking sand, which could contain iron impurities and aluminosili-
cates, rather than the glassmaking tools. The use of iron tools in glassmaking may well
affect the chemical composition of the glasses, but it is unlikely to do so in a regular
way: sample COR18 from Cordoba, which has higher iron by comparison with its
alumina content, is an example of a glass which may have been contaminated by metal
tools. Other possible sources for iron and alumina contamination include the refractory
materials (such as the crucibles) used during production, which could contribute a
small amount depending on the acidity of the glass and the properties of the crucible itself.
The presence of an excess of sodium chloride in our glasses could have been easily
solved by pre-treating the plant ashes, in order to remove the soluble sodium chloride,
but this may not have been common practice at the time. Pre-treatment of ashes such
as boiling to remove chlorides is mentioned in other historical texts,
but Don Cristóforo
himself does not mention it, which could imply that it was not done, or that the ashes were
procured by the glassmakers in a pre-treated state. In favour of the former explanation, we
might note that Münzer makes no mention of pre-treatment either, and he was present in
Alhama de Murcia itself, where the glassmaking plants grew and were gathered. Further-
more, the very need to remove a surface scum from the glass melt using a metal tool seems
to imply the presence of chlorides, and may be an argument against the pre-treatment of
the ashes at this time. This may have interesting implications for the export of the Spanish
plant ashes (barrilla), and the perceived difference in quality between ashes from the East
Mediterranean, preferred by the Venetians, and those from the Iberian Peninsula.
It is also interesting to note that the different qualities of glass described in the text seem
to specify a different ratio of silica to sosa: inma glass is three parts sosa and salicornia to
Duckworth et al., Electron microprobe analysis, 42.
E.g. Biringuccio, The Pirotechnia, 127.
one part sand or quartz pebbles; christillana is three parts sosa to two parts quartz pebbles;
physica is one part sosa to one part quartz. Given that we cannot be certain about the
origin of the recipe, it is worth considering that there may have been a substantial differ-
ence in the quality of the plant ashes used for the various qualities of glass. This is already
apparent in the fact that the salicornia plants are not used for the production of christillana
or physica, the two ner qualities of glass. Was there also a difference between the plant
ashes used for these two qualities? It is possible that Don Cristóforo was unaware of
this, if so. Another possibility is that the one to one ratio of plant ashes and quartz
pebbles in the physica glass produces a clearer glass (lower in impurities derived from
the plant ashes), but one that is less fast; i.e. that must be worked at a higher temperature
due to its lower quantity of temperature-reducing alkali. Interestingly, Don Cristóforos
assertion that the ner grades of glass include more silica echoes that of Münzer, who
notes that, If you wish to make white glass like crystal, it is necessary to add more ne
white sand …”.
This seems to conrm the practice, but it is also possible given the
many similarities between the texts that Don Cristóforo was aware of Münzers text
and used it as a source in his letter. The most effective way to investigate this in the
future would be to analyse a number of contemporary glasses, in order to test whether
there is indeed a lower soda content in the highest-quality glasses, which would
conrm the different ratio of plant ashes to silica suggested by the texts.
The use of lead in glass production may also provide a relevant angle of investigation,
particularly in terms of the transfer of technological practices. Don Cristóforo recounts the
use of lead in the production of smalti, which David Whitehouse, in reporting the text,
considers as enamel (coloured glass applied to the surface of glass or other materials),
but also coloured glasses used for other purposes (e.g. making jewellery by ame-
One pound of lead is added to ten pounds of the best quality physica glass.
He also advocates the addition of the ashes of tartar, meaning potassium bitartrate (KC
), which forms as a by-product of wine-making. By adding both lead and an alkali
(potassium), the coloured glass or enamel maker would lower the melting temperature
of the material, which would presumably aid in its application as enamel or use in
ame-working (lead can also combine with other oxides to produce vibrantly coloured
An understanding that lead softensglass by lowering its melting temperature may be
traced back to at least the Roman period, when the outer coating of cameo glass vessels was
made in a high-lead, white glass, which was easier to carve by comparison with the blue
glass beneath.
Perhaps more relevantly, there may yet prove to be some association of the
medieval addition of lead to glass with the Iberian Peninsula, particularly in the tenth and
eleventh centuries.
In this case, we can also trace some link between the glass and glazed
ceramic industries: the use of lead in glasses appears at around the same time as the devel-
opment of Iberian glazed ceramic production using lead (for example, at Madinat al-
Zahra). Later, the development of tin-glazes, so crucial to the production of Iberian lustre-
ware, was followed by the development of tin as a glass colourant: Don Cristóforo himself
Whitehouse, The Epistola Abbreviatora’”, 357.
Whitehouse, The Epistola Abbreviatora’”, 356.
Bimson and Freestone, The Portland vase and other Roman cameo glasses, 58.
Duckworth et al., Electron microprobe analysis,327; Duckworth et al., Non-destructive µXRF analysis,910.
explains how the addition of tin oxide produces an opaque white glass of superior
The primary production of glass in crucibles rather than larger structures, as described
by Don Cristóforo, is also signicant when considering which of our known glass pro-
duction remains could have been used for primary glassmaking.
Did the production
of glass from Don Cristóforosloavesbegin earlier than the fteenth century, and
what is the technological precedent of the pot furnace in the Iberian Peninsula? It
would certainly have been possible to make glass in some of the archaeologically identied
installations, such as the twelfth- to thirteenth-century furnace from Belluga (Murcia).
Glass production facilities can be difcult to interpret, as there is often very little in the
way of by-products; the skimming off of surface scum from the glass-melt as described
in the text may be one sign of primary glass production to watch out for in future research.
There is no mention of glass re-melting or recycling in Don Cristóforos text, although
it is explicitly mentioned in other sources: Theophilus describes the collection and re-
melting of antique glass as a means of colouring newly made glasses,
and Agricola
describes the re-melting of cast-off fragments from the glass-blowing process.
On the
other hand, the archaeological and compositional evidence for earlier centuries provide
very strong indications of recycling. For example, the results of chemical analysis of
glasses from ninth- to twelfth-century Malaga indicate that glasses of a mineral-alkali,
Roman-type composition were recycled together with plant ash glasses in south-east
From a technical perspective, the addition of small amounts of preformed glass
to the raw ingredients would help to ensure their fusion. The practice is not mentioned
by Münzer, either, so assuming for the moment that the two texts were unrelated
we may argue that it was less signicant in the fteenth-century glass industry than it
had been previously. By Don Cristóforos time, it was no longer possible to gather and
reuse vast quantities of Roman glass as had been practised extensively in Late Antiquity
and the early medieval period. Indeed, in the sixteenth century Biringuccio describes
antique glass as a rare curiosity, apparently mistaking corrosion patterns for the myster-
ious art of Roman glassmakers: At present I have near me a fragile piece of antique glass
of square form in which a very beautiful leaf pattern has been worked like tarsia, and it
has such a distribution of colours that I cannot understand how the articer made it so
beautifully and marvellously …”.
The need to produce larger quantities of primary
glass to meet the demand for window and vessel glass in the medieval period may well
have put paid to the large-scale practice of recycling.
Final thoughts
The comparison between the evidence of glass production recipes and the archaeological
and compositional evidence may raise more questions than it answers. But this is not to
say it is without value: indeed, the value of the process may be judged by the interest of the
Whitehouse, The Epistola Abbreviatora’”, 356.
Duckworth and Govantes Edwards, Medieval glass furnaces.
Córdoba, Technology, craft and industry, 110.
Theophilus, On Divers Arts, 59.
Agricola, De re metallica, 592.
Duckworth and Govantes-Edwards, La produccion de vidrio.
Biringuccio, The Pirotechnia, 131.
questions raised. Don Cristóforos text is an excellent example of the importance of recog-
nising assumed knowledge in technological treatises. In this case, the assumed knowledge
is that of furnace types and constructions, without which the production methods
involved will be difcult to ascertain. It is likely that these areas were dealt with by indi-
viduals who occupied a lower position in the professional hierarchy.
Two other key questions emerge from the comparison, and both will need to be
explored in greater depth in future research. First, what relationship was there between
the development of glassmaking in al-Andalus and the later southern European use of
plant ashes in glass production: did the Iberian industry have an inuence on the
Italian here, too, as it did in glazed ceramic production?
Second, what are the antece-
dents of the sorts of furnaces indicated here, in which glass production takes place in cru-
cibles, rather than in the large tanks known from Late Antiquity? Glass recycling may
provide an important temporal link between the larger- and smaller-scale glass making,
with the technology of adding alkalis to recycled glasses, for example, being eventually
developed in the Islamic world into a technology of producing primary glasses using
plant ashes and silica.
We expect to address these questions in future, with a continued programme of
research. Although this was a small-scale study, in which we have not tested all of the pro-
duction parameters, the combination of methodological approaches employed here
emphasises the value of approaching these various forms of evidence from a truly inter-
disciplinary perspective, enabling us to develop and eventually to answer new research
questions. These will feed into our understanding of trade, daily life, production and con-
sumption in the Iberian Peninsula and beyond.
The work involved in the production of this paper has beneted from different sources of funding,
for which we are most grateful. The work concerning medieval recipes was carried out within the
framework of the project El conocimiento cientíco y técnico en la Península Ibérica (siglos XIII-
XVI): producción, difusión y aplicacionesHAR 2012-37357 (Ministerio de Economía y Competi-
tividad), directed by author 3. The experimental work was carried out within the framework of
project Addressing the Invisible: Recycling Glass and Technological Practice in the 1
AD, British Academy Post-Doctoral Fellowship in the School of Archaeology and Ancient History,
University of Leicester, awarded to author 2.
Notes on contributors
David J. Govantes-Edwards is a professional archaeologist and student of philosophy; his research
focuses on the archaeological perspectives on technology from a theoretical point of view as well as
several aspects of the archaeology of al-Andalus. He is also directly involved in a number of research
projects, which include the Priniatikos Pyrgos Excavation Project (Crete, Greece), the Al-Andalus
Glass Project (Spain) and the Landscapes of Construction Project (Easter Island, Chile).
Chloë N. Duckworth, after being awarded her PhD (AHRC-funded) at the University of Notting-
ham, established an interdisciplinary research project and network (The al-Andalus Glass Project)
exploring glasses and glazed ceramics from the Muslim and Christian periods in the Iberian Penin-
sula. She has been involved in numerous archaeological projects in the UK, Iran, North Africa,
Komaroff, Color, precious metal, and re, 47.
Greece and Spain. Most recently, she was awarded a British Academy postdoctoral research fellow-
ship, which focuses on experimental and big dataapproaches to glass recycling in the rst mil-
lennium AD.
Ricardo Córdoba de la Llave, Professor at the University of Córdoba (Spain), focuses his research
on the way technical knowledge was transmitted during the Middle Ages, especially via the writing
of technical recipe books. In this regard, he has directed several international projects which include
the foremost specialists throughout Europe. He is also a central member of the al-Andalus Glass
Ricardo Córdoba
Bibliography of citations in the text
Agricola, Georgius. De re metallica. Trans. Herbert Clark Hoover and Lou Henry Hoover.
New York: Dover Publications, 1950.
Albertus Magnus. On the Causes of the Properties of the Elements. Trans. Irven Resnick. Milwaukee:
Marquette University Press, 2010.
Albertus Magnus. Book of Minerals. Trans. Dorothy Wyckoff. Oxford: Clarendon Press, 1967.
Alonso, María Pilar, Francisco Capel, Francisco Valle, Angel de Pablos, Inés Ortega, Blanca Gómez
and Miguel Ángel Respaldiza. Caracterización de un vidrio rojo medieval procedente de las
vidrieras del Monasterio de las Huelgas de Burgos.Boletín de la Sociedad Española de
Cerámica y Vidrio 48, no. 4 (2009): 17986.
Amasuno, Marcelino. En torno a las fuentes de la literature cientíca del siglo XIII: presencia del
Lapidario de Aristóteles en el alfonsí.Revista Canadiense de Estudios Hispánicos 9: 300328.
Barthélemy, Pascale. La Sedacina ou loeuvre au crible. Lalchimie de Guillaume Sedacer, carme
catalan de la n du XIV
siècle. Paris: S.É.H.A., 2002.
Bass, George, Berta Lledo, Sheila Matthews and Robert Brill. Serçe Limani. The Glass of an Eleventh-
Century Shipwreck. College Station: Texas A&M University Press, 2009.
Bazzochi, Francesca. Las vidrieras góticas mediterráneas: composición química, técnica y estilo. El
caso concreto de Barcelona y Siena en el siglo XIV. PhD diss, University of Barcelona, 2012.
Best, Michael, and Frank Brightman. The Book of Secrets of Albertus Magnus. Oxford: Clarendon
Press, 1973.
Bimson, Mavis, and Ian Freestone. An Analytical Study of the Relationship between the Portland
Vase and other Roman Cameo Glasses.Journal of Glass Studies 25 (1983): 5564.
Biringuccio, Vannoccio. The Pirotechnia of Vannocio Biringuccio.The Classic Sixteenth-Century
Treatise on Metals and Metallurgy. Trans. and ed. Cyril Stanley Smith and Martha Teach
Gnudi. New York: Dover Publications, 1990.
Carmona, Noemí, Ángeles Villegas, Pedro Jiménez, Julio Navarro and Manuel García-Heras.
Islamic Glasses from al-Andalus: Characterisation of Materials from a Murcian Workshop
(Twelfth Century AD, Spain).Journal of Cultural Heritage 10 (2009): 43945.
Carmona, Noemí., Manuel García-Heras, Cristina Gil and Ángeles Villegas. Vidrios y grisallas del
s. XV de la Cartuja de Miraores (Burgos): Caracterización y estado de conservación.Boletín de
la Sociedad Española de Cerámica y Vidrio 44, no. 3 (2005): 2518.
Córdoba, Ricardo. 2014 Technology, Craft and Industry.In The Archaeology of Medieval Spain
11001500, ed. Magdalena Valor and Avelino Gutiérrez, 10016. Shefeld: Equinox, 2014.
Córdoba, Ricardo. Un recetario técnico castellano del siglo XV: el manuscrito H490 de la Facultad
de Medicina de Montpellier.En la España Medieval 28 (2005): 748.
de Gayangos, Pascual. The History of the Mohammedan Dynasties in Spain. London: Oriental
Translation Fund, 1840.
Duckworth, Chloë. Imitation, Articiality and Creation: The Colour and Perception of the Earliest
Glass in New Kingdom Egypt.Cambridge Archaeological Journal 22 (2012): 30927.
Duckworth, Chloë, and David Govantes-Edwards. La producción de vidrio en Málaga en época
islámica. Nuevos datos.Mainake XXXV (forthcoming).
Duckworth, Chloë, and David Govantes-Edwards. Medieval Glass Furnaces in Southern Spain.
Glass News 38 (2015): 912.
Duckworth, Chloë, David Govantes-Edwards, Ricardo Córdoba, Laura Aparicio and Cristina
Camacho. El vidrio andalusí y su composición química: primeros resultados y posibilidades
de estudio.Boletín de Arqueología Medieval 18 (forthcoming).
Duckworth, Chloë, Ricardo Córdoba, Edward Faber, David Govantes-Edwards and Julian
Henderson. Electron Microprobe Analysis of 9
-twelfth Century Islamic Glass from
Córdoba, Spain.Archaeometry 57 (2015): 2750.
Duckworth, Chloë, Aurelie Cuénod and David Mattingly. Non-Destructive µXRF Analysis of
Glass and Metal Objects from Sites in the Libyan Pre-Desert and Fazzan.Libyan Studies 46
(2015): 1534.
Freestone, Ian, Nigel Meeks, Margaret Sax and Catherine Higgitt. The Lycurgus Cup a Roman
Nanotechnology.Gold Bulletin 40 (2007): 2707.
Frothingham, Alice. Spanish Glass. London: Faber and Faber, 1963.
Garcia Porras, Alberto. El azul en la producción ceramic bajomedieval de las áreas islámica y cristi-
ana de la Península Ibérica.In Atti del IX Congresso Internazionale Sulla Ceramica Medievale
Nel Mediterraneo. ed. Sauro Gelichi, 229. Florence: AllInsegna del Giglio, 2012.
Glick, Tomas. Islamic and Christian Spain in the Early Middle Ages. Princeton: Princeton
University Press, 1979.
Goody, Jack. The Logic of Writing and the Organisation of Society. Cambridge: Cambridge
University Press, 1986.
Henderson, Julian. Ancient Glass. An Interdisciplinary Exploration. Cambridge: Cambridge
University Press, 2013.
Jiménez, Pedro. El vidrio andalusí en Murcia.In El vidrio en al-Andalus, ed. Patrice Cressier, 117
48. Madrid: Casa de Velázquez, 2000.
Hill, Ronald, The Literature of Arabic Alchemy.In Religion, Learning and Science in the Abbasid
Period, ed. M.J.L. Young, E.D. Latham and R.B. Serjeant. Cambridge: Cambridge University
Press, 1990.
Isidore of Seville. The Etymologies. Trans. Stephen Barney and Muriel Hall. Cambridge: Cambridge
University Press, 2006.
Komaroff, Linda. 2004. Color, Precious Metal, and Fire: Islamic Ceramics and Glass.In The Arts
of Fire: Islamic inuences on glass and ceramics of the Italian renaissance, ed. Catherine Hess, 35
53. Los Angeles: The J. Paul Getty Museum, 2004.
Martínez Lorca, Andrés. Maestros de Occidente. Estudios sobre el pensamiento andalusí. Madrid:
Trotta, 2007.
Martinón-Torres, Marcos. Why Should Archaeologists Take History and Science Seriously?In
Archaeology, History & Science. Integrating Approaches to Ancient Materials,ed. Marcos
Martinón-Torres and Thilo Rehren, 1536. Walnut Creek: Left Coast Press, 2008.
Merrield, Mary. Original Treatises on the Arts of Painting. New York: Dover, 1967.
Morel-Fatio, Alfred, and Antonio Rodríguez. Relación del viaje hecho por Felipe II en 1585 a
Zaragoza, Barcelona y Valencia.Escrita por Henrique Cock. Madrid: Aribau, 1876.
Oppenheim, Alex, Robert Brill, Dan Barag and Axel von Saldern. Glass and Glassmaking in Ancient
Mesopotamia: an edition of the cuneiform texts which contain instructions for glassmakers with a
catalogue of surviving objects.The Corning Museum of Glass Monographs Volume III. Corning:
The Corning Museum of Glass Press, 1970.
Otte, Enrique. Sevilla y sus mercaderes a nes de la Edad Media. Sevilla: Fundación El Monte y
Universidad de Sevilla, 1996.
Pérez-Arantegui, Josena, and Carlos Pardos. Lustre Recipes for Hispano-Moresque Ceramic
Decoration in Muel (Aragón, Spain), or How Much a Little Copper Weighs.In
Archaeology, History & Science. Integrating Approaches to Ancient Materials, ed. Marcos
Martinón-Torres and Thilo Rehren, 15166. Walnut Creek: Left Coast Press, 2008.
Pfandl, Ludwig. Itinerarium Hispanicum. Hieronymi Monetarii. 14941495.Revue Hispanique
48 (1920): 1179.
Pollard, Mark, and Carl Heron. Archaeological Chemistry. 2nd ed. Cambridge: The Royal Society of
Chemistry, 2008.
Rodríguez, Sagrario. Lapidario: (según el manuscrito escurialense H. I. 15). Madrid: Gredos, 1981.
Smith, Cyril, and John Hawthorne. Mappae Clavicula. A Little Key to the World of Medieval
Techniques.Transactions of the American Philosophical Society 64 (1974): 3128.
Tanimoto, Satoko, and Thilo Rehren. Interactions between Silicate and Salt Melts in LBA
Glassmaking.Journal of Archaeological Science 35 (2008): 256673.
Theophilus Presbyter. On Divers Arts. The Foremost Medieval Treatise on Painting, Glassmaking
and Metalwork. Translated from the Latin with Introduction and Notes by John G.
Hawthorne and Cyril Stanley Smith. New York: Dover Publications, 1979.
Whitehouse, David. 2006. The Epistola Abbreviatoria: a Description of Glassmaking in
Reinaissance Spain.In Annales of the Seventeenth Congress of the International Association
for the History of Glass, ed. Koen Janssens, Patrick Degryse, Peter Cosyns, Joost Caen and Luc
Vant dack, 3558. Antwerp: ASP.
Young, M.J.L., and R.B. Latham. Religion, Learning and Science in the Abbasid Period. The
Cambridge History of Arabic Literature. Cambridge: Cambridge University Press, 1990.
Bibliography of relevant technical treatises
Agricola, Georgius. De re metallica. Trans. Herbert Clark Hoover and Lou Henry Hoover.
New York: Dover Publications, 1950.
Albertus Magnus. On the Causes of the Properties of the Elements. Trans. Irven Resnick. Milwaukee:
Marquette University Press, 2010.
Albertus Magnus. Book of Minerals. Trans. Dorothy Wyckoff. Oxford: Clarendon Press, 1967.
Alfonso X Rey de Castilla. Lapidario.
Barthélemy, Pascale. La Sedacina ou loeuvre au crible. Lalchimie de Guillaume Sedacer, carme
catalan de la n du XIV
siècle. Paris: S.É.H.A., 2002.
Biringuccio, Vannoccio. The Pirotechnia of Vannocio Biringuccio. The Classic Sixteenth-Century
Treatise on Metals and Metallurgy. Trans. and ed. Cyril Stanley Smith and Martha Teach
Gnudi. New York: Dover Publications, 1990.
Celaya, J. [?] Manuscript H-490. lÉcole de Medicine, Montpellier University.
Isidore of Seville. The Etymologies. Trans. Stephen Barney and Muriel Hall. Cambridge: Cambridge
University Press, 2006.
Neri, Antonio, The Art of Glass. Ed. Christopher Merrett and Michael Cable. Shefeld: Society of
Glass Technology, 2001.
Pliny. Natural History.
Theophilus Presbyter. On Divers Arts. The Foremost Medieval Treatise on Painting, Glassmaking
and Metalwork. Translated from the Latin with Introduction and Notes by John G.
Hawthorne and Cyril Stanley Smith. New York: Dover Publications, 1979.
... However, these papers mostly aim to retrieve the dating or region of production of the objects [24][25][26][27]. For stained-glass windows, we found a single and very recent reference suggesting the existence of a relation between the quality of the materials with the iconography. ...
... The results are expressed in wt% for the major and minor elements (K 2 O, CaO, MnO, and Fe 2 O 3 ) and in ppm for the trace elements (Co, Cu, Rb, Sr, Zr, and Ag). Corning standards correspond to given data from [25] and NIST standards to given data from [26]. Table S2. ...
Full-text available
The understanding of the connection between the value of an image and the value of the materials that were used to make it is limited, especially for stained-glass windows. However, such information can bring-to-light how artistic and economic questions were intertwined and how the final artwork depended on the ranking of the materials. With this paper, we aim to illustrate the benefit of combining art historical research with scientific analysis to retrieve the selection of the quality of the materials of stained-glass windows. Therefore, the main objective of this paper is to investigate the link between the materials and the iconography in order to recover artistic choices and highlight a possible hidden symbolism for a set of window panels, used as a first case-study. Glass quality is investigated according to the following parameters: (1) the glass composition, (2) the glass forming technique, (3) the transparency and hue of the colourless glass, and (4) the rarity and complexity of the colouring technology. The results of our research indicate that the four-studied panels were originally assembled from two different glass compositional groups, K-rich glass and Ca-rich glass, and that specific attention was paid to select only high-quality materials and production techniques for the representation of the characters with higher positions in the religious hierarchy. A very interesting aspect concerns the way the bishop was rendered in one of the panels, because it seems that he actually upgraded his own prestige by requesting the use of specific materials and more attentiveness to his rendering in the panel. By this research, we proposed a first case-study with a non-destructive tool to bring a discussion on the use of different glass qualities in stained glass window. We hope to further encourage such studies on window panels across Western Europe to verify if similar observations can be made.
... In the Iberian Peninsula, Medieval glass recipes were spread in different technical treatises. 4 Among them, the Manuscript H-490 is one of the most prominent. 5 Juan de Celaya, the supposed author, worked in the University of Salamanca, the oldest university in Spain and the third oldest university in the world, and he could have made the compilation between 1460 and 1480. ...
... 7 By contrast, a recipe from the treatise Epistola Abbreviatora, written by Don Christ oforo of Soto Mayor in the 16th century, was attempted but not successfully reproduced. 4 The main objective of this work was the interpretation, reproduction, and characterization of the four recipes for glass from the Manuscript H-490 preserved in the l' Ecole de M edicine of Montpellier University (France). These experiments bring new insights into the technique of medieval glass production, demonstrating the high impact of such a transdisciplinary methodology for the study of historical materials. ...
The research on manuscripts provides useful information about the artistic/technical production and the scientific development in the past. However, the reproduction of the ancient recipes is difficult because most of them are described generally or they hide essential information to preserve the production secrets. In this study, four different recipes from the medieval Manuscript H‐490 (École de Médicine of Montpellier University, France) were reproduced. The raw materials and the production process of each recipe were discussed from the point of view of the glassmaking, and the final products were characterized. The recipe (31) indicated the preparation of a white glaze, similar to Islamic frits. The recipes (32) and (33) explained the preparation of an “unbreakable” glass; however, the characterization of the final products showed that no changes in the hardness of the glass were obtained. And the recipe (34) described the preparation of a green glass which was successfully obtained. This article is protected by copyright. All rights reserved.
... Moreover, the permeability between Christians and Muslims was dynamic and the Islamic influence in the production technology of other materials is undeniable, as is the case with lusterware. As already noted [16], this interconnection and transfer of technology is never restricted to one sole craft. ...
Full-text available
A set of 14 glass fragments and production remains dated to the 16th and 17th centuries was collected during rescue archaeological works conducted in Granada, Spain, and was characterised by µ-PIXE. This preliminary study constitutes the first analytical approach to glass manufacturing remains from a Spanish production dated to the early-modern period. µ-PIXE allowed for the quantification of major, minor and some trace elements of the glass fragments. It also allowed mapping the elemental distribution on the fragments that were identified as an interface of crucible/glass. This analysis constitutes an evaluation of the ionic exchange between glass and crucible. The glass colours vary from the natural green and blue hues to completely colourless samples. The results show that the majority of the glass samples are of soda-lime-silicate composition, and only one proved to be of a potassium-rich composition. From this, one can hypothesise that glass rich in sodium (following the Mediterranean tradition) and potassium-rich glass (following a central and north European tradition) were both locally produced. Since this location was known as la Calle Horno del Vidrio (Glass Furnace Street) and several production evidences were found, it is highly probable that an artisanal glass production existed in this area.
... The study of the recipes from arcana presents the most promising way to gain knowledge about the historical glass production. [15][16][17][18] There are several batch books that belonged to glassmakers in regions such as the British Isles (as revealed by Colin Brain in a private oral communication), the United States of America (as can be consulted at the Rakow Research Library of Corning Museum of Glass), France, 19 and Spain 20 among others. In Portugal, there are three known arcana with a chronology dated to between the 18th and the 20th centuries. ...
The present work aims to study the glasses commonly named crystal glass produced in Portuguese factories from the 18th to the 20th centuries through their arcana or batch books. Recipes for colourless crystal glasses were selected, analysed and reproduced in the laboratory. Five recipes were chosen from the Marinha Grande arcanum, five recipes from the Gaivotas’ Factory arcanum and three recipes from the Castro e Oliveira Guerra arcanum. In order to characterize the composition and thermal‐physical properties of reproduced glasses, different analytical techniques were used such as micro energy dispersive X‐ray fluorescence, µ‐ Raman spectroscopy, differential scanning calorimetry, dilatometry, Vickers hardness, optical microscopy and UV‐Vis absorbance spectroscopy. The selected recipes were proven viable for reproduction and the obtained glasses presented good thermal properties that allow the workability and creation of objects. It was also proven that there is a similarity in terms of chemical composition to some of the historical glasses attributed to Portuguese production in Portuguese museums.
The early modern period is mainly characterised by High Lime-Low Alkali (HLLA) glass, a lime-rich glass made from plant or tree ashes, originating from 14th-century Germany and later used all over Europe. Attempts to link HLLA chemical subgroups to a particular point in time have failed so far. Driven by a request from the archaeological community, our research group has been exploring the feasibility of UV–Vis-NIR absorption spectroscopy as a non-destructive and in-situ applicable analysis technique for more than a decade. The main goal of this research is to provide a better understanding of the subgroups of HLLA glass and their respective dating via non-destructive means. A second topic relates to the role of cobalt as a potential indicator for either the type of applied ashes or for glass recycling. In this paper, we present the UV–Vis-NIR and LA-ICP-MS results of a total of 45 HLLA colourless glass objects or fragments, supplemented with three blue glasses from the 15th to the 17th centuries. First, we observed a correlation between iron and cobalt contents and that these two elements show more elevated concentrations starting from the middle of the 16th century. Different types of sources can be responsible, such as the type of raw materials, the tools employed, and recycling. We hypothesised that both elements were introduced through the wood or plant ashes used as fluxing agent. Then, we noted that the presence of low amounts of cobalt in colourless glass, can be observed through the analysis of the Co²⁺ absorption bands in the optical spectra down to 18 ppm. Next, we describe an approach to quantify iron and cobalt from the optical spectra and to date HLLA material by means of absorption spectroscopy, a valid, rapid, and non-destructive alternative for laboratory measurements. Finally, we show that the optical parameters (the Ultra-violet Absorption Edge (UVAE), the calculated Fe²⁺ and total iron contents, and the Co²⁺ absorption bands characteristics) allow discerning two glass groups: one dating to the end of the 15th-middle of the 16th centuries, and the other to the second half 16th-17th centuries. These results gain valuable information to further resolve the study on recycling, on the influence of the glassmaking tool on the glass batch composition and/or on the selection or treatment of the raw materials in HLLA glass.
This introductory article offers an in-depth discussion of the special issue’s overall theme, as well as summaries of the individual contributions and a reflection on how digital tools are reshaping research. The first section covers the recent flourishing of large-scale digitization projects along with advances in material sciences and in a range of scholarly disciplines including paleography and codicology, art history, musicology, literary studies, and conservation and restoration, all of which have explored previously unimaginable possibilities for the study of medieval manuscripts. The second section focuses on the articles gathered for the special issue: those helping to create a theoretical framework, those presenting the results of recent projects, and a group of case studies that reveal how scholars are gradually adopting digital technologies and material studies as essential research tools. The third and final section suggests new avenues of investigation and methodological approaches to promote and improve our current understanding of Iberian manuscript materiality.
This work examines the interdisciplinary methodology currently used to study medieval technical manuscripts and recipe books from the Iberian Peninsula. The methodology is based on both formal and content analysis, including classic paleographic and codicological approaches and the use of scientific techniques on the physical medium, including parchment or paper, inks and pigments, and covers. From the point of view of content, the technical procedures described in the Hispanic recipes can be compared to those presented in other European texts and the technical literature of other historical periods. Not only has this yielded excellent results, but it has also allowed the experimental reproduction of the processes described in these recipes, permitting researchers to verify their validity and to reproduce forms of medieval knowledge with possible applications in the twenty-first century.
How might an interdisciplinary approach involving experimental archaeology improve our knowledge of glassmaking in medieval Iberia? Our current limited understanding lacks an appreciation of how surviving remains were created through the actual practice of glassmaking—herein lies the biggest single gap in knowledge. Archaeological experiments show that while the infima glassmaking recipe offers a credible guide to basic glassmaking technology, it is best interpreted as a set of learned instructions rooted in, though not describing, workshop practice. Awareness of the sensory qualities of glass, the conducting of experiments, and observation of glass production practice, all combined within a theoretical framework that embraces embodied knowledge and phenomenological aspects of space and time, suggest the potential existence of an encoded “text” of past glassmaking practice within archaeological workshop remains. The authors advocate further experimental archaeology on a more ambitious scale, exploring the sensory and performative aspects of glassmaking practice, to better learn to read the distinctive handwriting of this “text” in medieval Iberian archaeology.
This paper examines glassmaking in medieval Iberia from the point of view of technical literature, especially recipe books and alchemical treatises, in an attempt to assess to what extent this literary genre (if it is to be defined as such) may have affected, or have been affected by, technological developments in glassmaking between the eighth and sixteenth centuries. Iberian technical literature on the making of glass is put in connection with broader European and Mediterranean trends in the transmission of technical knowledge, the nature of scribal culture and the impact caused by the dissemination of the printing press. Ultimately, the paper aims to review the relationship that exists between the authors of technical literature and contemporary workshop practice, not only taking the written word as evidence, but also using the understanding provided by other fields of research, such as the study of the chemical characterization of medieval glass.
This special issue, “Looking ahead: new approaches to medieval Iberian heritage”, is the main output of a fruitful collaboration between the humanities and the experimental sciences, which has greatly contributed to increase our knowledge of creative processes in medieval Iberia. The articles examine a wide range of objects produced using very different media, such as illuminated manuscripts, glass, monumental painted altarpieces and azulejos (glazed tiles). Some of these objects were studied for the first time in the framework of this project, while others had received very little attention previously. Moreover, several of the case studies concern unfinished works, which gives us an opportunity to better approach the creative processes. This introductory article aims to establish the main overarching themes that have emerged from the joint efforts of the participating scholars and teams. These themes include the multicultural context of medieval Iberia, a revision of the traditional notion of the medieval workshop, a consideration of the materials used to construct colours and molecular palettes, and the transfer of technological processes between the different cultural and religious horizons that coexisted in the Iberian Peninsula. This paper also investigates the new avenues of research that the articles have opened, such as the role played by medieval Iberia in a broader European, Mediterranean and global context regarding the arrival of precious materials from the Far East.
Full-text available
Twenty-six samples from domestic assemblages of 9th–12th century Córdoba were subjected to electron microprobe analysis. The results reveal two main compositional types. The first, encountered in 13 of the samples, seems to result from the combination of plant ashes with high-impurity sand, and has some contemporary parallels from Syria and Egypt. The second type is a lead–soda–silica glass, encountered in a relatively high proportion of the glasses (11 of the 26 sampled), possibly formed by the addition of lead metal to existing glasses and with very few known parallels. These are among a very small number of results available to date on the chemical composition of glasses from medieval Spain, and the presence of a high proportion of lead–soda–silica glasses is particularly interesting, possibly indicating a technological practice unique to, or originating in, the western Muslim world.
The five centuries of the 'Abbasid period (eighth to thirteenth centuries AD) were the golden age of Arabic literature. They saw the appearance not only of poetry and belles-lettres (which are covered in a previous volume), but also of an extensive body of writings concerned with subjects ranging from theology and law to history and the natural sciences. This volume of The Cambridge History of Arabic Literature surveys the most important of these writings, including the literature of Sunnism and Shi'ism, Arabic philosophy, Sufism, Islamic law, grammar, lexicography, administration, historiography, mathematics, astronomy, astrology, geography, alchemy and medicine. It contains separate chapters on six of the greatest scholars of the Middle Ages, as well as on the Arabic literature of the Christians and Jews who lived under the rule of the 'Abbasid caliphate, and includes a study of one of the great cultural movements of the period, the translations from Greek into Arabic.
Figures, Tables and Maps Introduction Part One Society and Economy 1. At the Crossroads of Civilization 2. Agriculture, Settlement and the Moving Frontier 3. Urbanization and Commerce 4. Social Structure 5. Ethnic Relations 6. Structure and Stability Part Two Movement of Ideas and Techniques 7. Technology 8. Science 9. Cultural Process in Medieval Spain Bibliography Index
This paper reports on the non-destructive analysis of 42 samples of copper alloy and glass from sites in Libya, using semi-quantitative μXRF, carried out as part of the work of the Trans-Sahara Project funded by the European Research Council. These are among the first chemical analyses to be performed on metals and glasses of any period found in Libya, and the results – though preliminary – raise some interesting possibilities. In particular, we discuss some possible indications with regard to the practice of recycling glasses, as evidenced through heterogeneous, malformed glass beads with variable quantities of lead. A glass mirror from Ghirza was also found to be backed in lead, and was probably the result of a glass-making technique still practised in recent times in India. The metal analysis has revealed evidence of a pre-Islamic trade in brass in the northern Sahara, as well as showing the presence of objects made from the mixing of different types of scrap metal, a process probably taking place at the Garamantian metalworking site of Saniat Jibril among other locations. The importance of further analysis of available Libyan and other North African metal artefacts and glasses for the contextualisation and extension of these findings is emphasised.
The introduction and use of glass in Late Bronze Age Egypt (18th to 19th Dynasties) is discussed from a materiality-based approach. It is suggested that the artificiality of this new material was deliberately proclaimed, highlighting the ability of those behind its production to access the processes of creation and transformation. Colour is central to the arguments presented, and it is suggested that glass was valued for its ability to fully assume particular colours, rather than displaying these on the surface only in the manner of painted, glazed or gilded artefacts.
Rescue archaeological excavations at an urban glass workshop of the 12th century AD in the city of Murcia (Spain) have provided one of the few evidences of glass production in the ancient Islamic territory of Al-Andalus. This paper reports the results derived from a chemical–physical characterisation study carried out on a representative sample set of glass fragments and industrial debris from that workshop. The main objectives of the research were to contribute to the knowledge of the type of glasses produced and provide some insights into the technology developed to obtain different colours in glasses. The resulting data indicated that both high-magnesia plant ash (HMG) soda-lime-silicate and soda-lime lead-silicate glasses were produced. They also indicated a deep knowledge of glass colouring techniques, which suggests that a careful control over the glass melting processes was achieved. Among others, the occurrence of bulk-coloured silver yellow and copper ruby red transparent glasses prove the skills reached by Murcian glassmakers. These results shed new light on the Islamic glass technology of a geographical area in which, up to now, little compositional and technological data from glass workshops were available.