Content uploaded by Yvonne Shashoua
Author content
All content in this area was uploaded by Yvonne Shashoua on Feb 01, 2019
Content may be subject to copyright.
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=ysic20
Download by: [Det Kongelige Danske Kunstakademis skoler for Arkitektur, Design og Konservering],
[Yvonne Shashoua]
Date: 20 September 2016, At: 00:25
Studies in Conservation
ISSN: 0039-3630 (Print) 2047-0584 (Online) Journal homepage: http://www.tandfonline.com/loi/ysic20
Mesocycles in conserving plastics
Yvonne Shashoua
To cite this article: Yvonne Shashoua (2016) Mesocycles in conserving plastics, Studies in
Conservation, 61:sup2, 208-213, DOI: 10.1080/00393630.2016.1168074
To link to this article: http://dx.doi.org/10.1080/00393630.2016.1168074
Published online: 19 Sep 2016.
Submit your article to this journal
View related articles
View Crossmark data
Mesocycles in conserving plastics
Yvonne Shashoua
Environmental Archaeology and Materials Science, National Museum of Denmark, Kongens Lyngby, Denmark
Analysis suggests that progress in conservation of plastics objects and artworks can be described by a
series of overlapping mesocycles. Focus has been placed for periods of 5–10 years each on determining
the degradation pathways in the 1990s, developing strategies to inhibit those pathways from the late
1990s and, since 2006 on actively stabilizing and treating the symptoms of degradation. The primary
driving forces behind the direction and rate of progress within each of these three mesocycles have been
different and specific. The controlling factor in understanding degradation pathways for heritage plastics
has been the origin of the data describing lifetimes. By contrast, mesocycles in developing suitable
storage and display microclimates for plastics have mirrored preventive conservation practices for natural
polymeric materials. The rate of the third mesocycle, interventive conservation, has been driven by the
need to balance the requirements for reversibility in conservation practices with the artist’s intent and
significance. Developments within each of the three mesocycles from the 1990s to date are discussed in
this article. Environmental science and toxicology of waste plastics offer a novel source of information
about real time degradation in terrestrial and marine microenvironments that seems likely to contribute to
the conservation of similar materials in contemporary artworks.
Keywords: Plastic, Conservation, Degradation, Preventive conservation, Interventive conservation, Mesocycle
Introduction
Plastics have short lifetimes compared with those of
traditional materials found in heritage collections,
and exhibit visible symptoms of degradation between
5 and 35 years after acquisition. The challenges
raised by the deterioration and conservation of plastics
in museums and galleries have been recognized for-
mally since 1991 largely as a result of the international
conference ‘Saving the Twentieth Century: The
Conservation of Modern Materials’organized by the
Canadian Conservation Institute and held in
September of that year (Grattan, 1993). The 36
papers presented at the conference focused on identify-
ing the signs of degradation exhibited by early, semi-
synthetic plastics and rubbers in design, ethnographic
and military collections. The International Council of
Museums Committee for Conservation (ICOM-CC)
established the working group ‘Modern Materials
and Contemporary Art’in 1996 to discuss and docu-
ment degradation pathways, conservation theory and
practice for modern materials. Today, it numbers
more than 200 members and is one of the largest in
ICOM-CC.
Progress in conservation of plastics objects and art-
works is often perceived as slower than that of
traditional heritage materials, but deeper analysis
suggests instead that its progress cannot be described
by a steady, linear path but by a series of overlapping,
5–10 year mesocycles. Periodization is a systematic
planning of physical training developed by Hans
Selye and has been used widely by sports professionals
since the 1950s (Rowbottom, 2000). Its purpose is to
achieve the best possible outcome for a specific compe-
tition, by progressively cycling various aspects of
training. Progress in conservation of plastics and art-
works from the early 1990s can similarly be described
in terms of periodization. The purpose of the macro-
cycle in sport is to peak for the goal competition of
the year, and it comprises 3 or 4 progressive meso-
cycles (Fig. 1). The purpose of the macrocycle in plas-
tics conservation is to prolong the useful lifetime of the
material and its significance for future generations. In
sport, a mesocycle is defined as a period in which the
focus is on specific areas, for example muscle mass.
During the developmental history of plastics conserva-
tion, focus has been placed for periods of 5–10 years
each on researching and publishing on degradation
pathways in the 1990s (Shashoua & Ward, 1995),
developing strategies to inhibit degradation from the
late 1990s (Shashoua, 2003) and, since 2006 on
actively stabilizing and treating the symptoms of
degradation (Fig. 2).
The primary driving forces behind the direction and
rate of progress of research or conservation practice for
Correspondence to: Yvonne Shashoua, Environmental Archaeology and
Materials Science, National Museum of Denmark, IC Modewegsvej –
Brede, DK-2800 Kongens Lyngby, Denmark.
Email: yvonne.shashoua@natmus.dk
© The International Institute for Conservation of Historic and Artistic Works 2016
Received January 2016; revised paper accepted March 2016
DOI 10.1080/00393630.2016.1168074 Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-208
each of these three mesocycles have been different and
specific. The controlling factor in understanding
degradation pathways for heritage plastics has been
the origin of the data describing lifetimes. By contrast,
mesocycles in developing suitable storage and display
microclimates for plastics have mirrored preventive
conservation practices for natural polymeric materials.
The rate of the third mesocycle, interventive conserva-
tion, has been driven by the balance between reversi-
bility in conservation practices and retaining original
artist’s intent and significance. Developments within
each of the three mesocycles are discussed in this
article together with proposals for future directions.
Mesocycles in understanding degradation of
plastics
Prior to designing a conservation strategy for modern
artworks or objects, it is essential to understand the
causes and extent of degradation of its component
materials. Although plastics products and designs
were available for the first time in the 1940s, their
instability was not recognized by the plastics industry
until 20 years later (Morgan, 1994). Previously, symp-
toms of degradation were often attributed to product
misuse by their owners. When owners of armchairs
covered with Naughahyde plasticized polyvinyl chlor-
ide (PVC) in the 1950s complained to the manufac-
turer that the armrests became sticky with time, they
were informed that their personality was not suitable
to own the new fake leather furniture (Kanigel,
2010)! Based on current knowledge, it seems more
likely that stroking the PVC upholstery accelerated
the diffusion of sticky, liquid phthalate plasticizers to
surfaces.
The Historical Plastics Research Scientists Group
(HPRSG) was formed in 1993 in the UK with the
purpose of establishing the degradation pathways of
plastics in museum collections. HPRSG invited indus-
trial polymer chemists to be members because it was
assumed that experts in making and evaluating the
performance of plastics would also be experts in
their breakdown processes. Condition surveys of
more than 700 plastics objects in the Victoria &
Albert Museum, London, UK, and the British
Museum, London, UK, collections indicated that
degradation was detectable by appearance, odour or
feel 5–25 years after production (Then & Oakley,
1993). One of the most unstable plastics identified
was PVC, among the most highly consumed plastics
worldwide.
Publications by the plastics industry describe the
major symptoms of degradation as darkening and for-
mation of hydrogen chloride. By contrast, surveys by
HPRSG members reported stickiness and shrinkage
due to loss of plasticizer from PVC as the major degra-
dation pathway. The difference in pathways may be
explained by the different ageing environments.
Service lifetimes of industrial plastic products are
determined from a change in weight, dimension or
colour when the material is exposed to 60 or 98°C
Figure 1 Example of structured mesocycles in periodized sports training showing the volume as bars and intensity as a line of a
20-week periodized mountain bike training plan. Reproduced from http://www.sciencetosport.com/periodization/with
permission.
Figure 2 The three mesocycles in the development of
conservation of plastics, reflected by the number of peer-
reviewed articles from the 1990s to date. The trend lines for
each mesocycle show the focus periods for research into
degradation of plastics (black line), preventive conservation
(green line) and interventive conservation (red line).
Shashoua Mesocycles in conserving plastics
Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-209
for a period between 7 and 30 days. The results are
extrapolated to ambient conditions or real time
(Table 1).
H.M. Quackenbos, an industrial chemist, defined the
lifetime of plasticized PVC as the period required for
10% of its original weight to be lost (Quackenbos,
1954). Extrapolating from thermal ageing at 98°C, he
concluded that lifetimes for plasticized PVC films
ranged from 3 months to 1000 years at ambient
temperatures. Because PVC was first available in the
1920s, materials that have undergone real time ageing
for 1000 years are not yet available, but the mismatch
between symptoms of degradation and lifetimes deter-
mined by conservators and industry is already clear.
The realization that industry’s approach to deter-
mining the lifetime of plastics could not be directly
applied to heritage materials initiated a new develop-
mental mesocycle around 2005. Growing interest in
plastics conservation at the start of the twenty-first
century resulted in increased funding for multidisci-
plinary, national and Europe-wide research projects,
conferences, training in identification and conserva-
tion of plastics and publications. Such activities have
enabled conservation professionals to share and
compare their experiences of degradation and lifetimes
of plastics rather than being dependant on the plastics
industry. The conference, ‘Plastics: Looking at the
Future and Learning from the Past’in 2007 highlighted
two effects on acquiring artworks and their conserva-
tion which are the direct result of interaction between
museums and artists. Firstly, museums and art galleries
consider whether to acquire artworks which are
intended to be ephemeral and therefore likely to
require extensive conservation resources (Coles, 2007).
Secondly, some artists are willing to investigate the
long-term stability of specific plastics prior to selecting
their working materials (Wel ls, 2007).
The fate of waste plastics offers a novel source of
information about real time degradation in terrestrial
and marine microenvironments (Fig. 3). Environmental
scientists are presently determining the sources and
concentration of microplastics (1–5 mm in diameter)
in the Mediterranean Sea (Cózar et al., 2015),
oceans and in African lakes, and the author is cur-
rently contributing experience of the breakdown of
plastics to two such projects (Biginagwa et al., 2016).
Microplastics enter the food chain via micro-organ-
isms and fish. Data about degradation pathways of
plastics in real time and the factors which control
their rate can contribute to our understanding of iden-
tical materials in heritage collections.
Mesocycles in preventive conservation of
plastics
The earliest studies suggested that the least stable plas-
tics produced volatile, acidic degradation products that
attacked other materials in the vicinity. As a result, cel-
lulose nitrate (CN), cellulose acetate (CA), PVC and
polyurethanes earned a reputation as ‘malignant plas-
tics’(Williams, 2002). Degrading Pedigree™dolls
dating from the 1950s comprising CA were described
as ‘sick, diseased and infectious’(Edwards et al.,
1993). As a result, the first preventive treatments
involved both isolating them from other, ‘healthy’
materials and ventilating them to reduce the risks of
autocatalytic degradation (Quye, 1999). Guidelines
designed to preserve other fragile organic materials
such as feathers and plant fibres were applied to plas-
tics. These included maintaining a stable relative
humidity, usually 55 ±3% at 18 ±2°C, light levels
Figure 3 Degraded waste plastics are good models for
museum plastics. (a) A latex rubber glove after six months on
a beach on the west coast of Denmark. (b) A latex rubber
glove after 60 years in the collections of The Royal Danish
Arsenal Museum.
Table 1 Major categories of use and expected lifetimes of
industrial PVC products in Europe based on accelerated
ageing and extrapolation to real time. Source: European
Union Commission (2000).
Category
Example of
application
Average lifetime
(years)
Building Window frames 10–50
Packaging Film and sheet 1
Furniture Fake leather
upholstery
17
Household
appliances
Tubing 11
Electric and
electronic
Cable insulation 21
Automotive Steering wheel
cover
12
Others Blood bags 2–10
Shashoua Mesocycles in conserving plastics
Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-210
around 50 lx and active ventilation. Meeting this diffi-
cult and costly challenge led to the next developmental
mesocycle.
In the mid-1990s, adsorbents designed to remove
volatile materials offgased by degrading objects
became commercially available to conservators
(Grzywacz & Tennent, 1994). Zeolites, hydrated alu-
minosilicates, were included in conservation packing
to inhibit degradation of CA by adsorbing both
acetic acid and water. Activated carbon was used to
inhibit the degradation of CN by adsorbing nitrogen
oxide thus preventing autocatalysis (Ward &
Shashoua, 1999). Although silica gel is most fre-
quently used in conservation practice to adsorb
water vapour, it can also adsorb formaldehyde and
acetic acid (Kopaç & Kocabas¸, 2002). Recent research
by the author suggests that, although general adsor-
bents are used to inhibit the degradation of plastics,
they are poorly specific (Shashoua et al., 2014).
Desorption of zeolites after exposure to CA suggests
that water, acetic acid and diethyl phthalate plasticizer
compete for space in the zeolite pores because of their
similar diameters. Loss of plasticizer causes shrinkage.
Ranking effectivity of adsorbents to inhibit degra-
dation from most to least gave the sequence: archival
cardboard, Corrosion Intercept
®
, zeolite 4 Å, acti-
vated carbon and silica gel (Fig. 4). This suggests
archival cardboard boxes to be more effective than
using general adsorbents.
Increasing energy costs combined with pressure to
implement sustainability in conservation since the
start of the twenty-first century have been the driving
forces to replace HVAC and adsorbent systems with
low-technology alternatives (O’Dwyer, 2010). Storing
plastics objects at temperatures below 10°C has been
proposed as a low cost, maintenance-free technique
for slowing the rate of most chemical degradation reac-
tions (Michalski, 2002). In addition, reducing the
temperature from ambient to that of a domestic
freezer reduces the rate of diffusion of plasticizer
from PVC by a factor of fifteen (Shashoua, 2004).
Initial findings of a pilot study on the effect of cold
storage on physical properties of plastics suggest that
storage in a domestic freezer should be considered as
a sustainable alternative to the present preventive con-
servation options for plastics (Shashoua, 2005).
Mesocycles in interventive conservation of
plastics
Established treatments for cleaning and adhering plas-
tics are few compared with their preventive conserva-
tion equivalents, because they were developed later
(Laganá & van Oosten, 2011). The well-known book
Plastics collecting and conserving published in 1999
contains chapters on surveying plastics, analysis,
degradation and preventive conservation but no guide-
lines for interventive treatments. This omission may be
attributed to the challenge presented by the high sensi-
tivity of deteriorated plastics to physical forces and
organic liquids used in interventive treatments, which
increase the risk of irreversible changes. Another
explanation is that until the start of the twenty-first
century, more scientists than conservators researched
plastics and preventive conservation was more appro-
priate to their skill sets.
Growing interest in exhibiting and collecting plas-
tics in art and design from the end of the twentieth
century has increased pressure on conservators to
develop techniques to clean, adhere and retouch
them. Although surveys of the condition of museum
collections containing plastics in the United
Kingdom, Scandinavia and the Netherlands conclude
that approximately 75% of collections require clean-
ing, the practice has been poorly developed largely
due to the risk of scratching plastics. Another risk of
cleaning rigid plastics such as polystyrene and
Figure 4 Acetic acid and diethyl phthalate plasticizer
adsorbed from exposure to undegraded (blue) and degraded
(red) cellulose acetate films. Adsorption of acetic acid slows
the rate of degradation while adsorption of plasticizer
induces shrinkage.
Figure 5 Crash test dummy child was effectively cleaned of
plasticizer and soil using Orvus WA paste and microfiber
cloth. ©Science Museum, London. Photo: Katherine Segal.
Shashoua Mesocycles in conserving plastics
Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-211
polymethyl methacrylate with solvents is environ-
mental stress cracking, which causes development of
white crystalline structures (Fenn, 1993). Stress crack-
ing is irreversible and may occur either immediately
after application of solvent or may develop gradually
after weeks or months.
Established guidelines for cleaning traditional, vul-
nerable heritage materials recommend using dry
brushes to remove dirt and limit damage. Findings
from the EU 7th Framework research project
Preservation Of Plastic ARTefacts in museums
(POPART) concluded that the water in moistened
microfibre cloths and tissues, lubricated plastics sur-
faces and minimized scratches (Fig. 5). Two-propanol,
commonly known as isopropanol was both effective at
removing oily, organic dirt and unlikely to induce
stress cracking whereas acetone was most frequently
associated with irreversible damage. POPART has
changed cleaning practice.
Developing new techniques and materials to conso-
lidate crumbling and collapsing degraded poly-
urethane foams such as those present in sculptures
by Piero Gilardi from the 1960s has been a focus
area for conservation. Applying Impranil™DLV, a
polyester/polyether urethane dispersion combined
with light stabilizers by nebulizer has been established
as an effective treatment (Van Oosten, 2011).
Although clearly irreversible, the treatment protects
the residual physical properties of the material. The
EU Horizon 2020 research project Nanomaterials
for the Restoration of Art (NanoRestArt) launched
in June 2015 is the first large, European-wide initiative
to develop and evaluate polyfunctional nanomaterials
for cleaning, coating and reintroducing lost plasticizers
to degraded plastic artworks.
1
Conclusions
Progress in conservation of plastics objects and art-
works cannot be described by a steady, linear path
from its origin in 1991 to today, but by a series of
mesocycles during which conservation professionals
have re-examined conservation strategies before updat-
ing or replacing them. Focus has been placed for
periods of 5–10 years each on determining the degra-
dation pathways in the 1990s, developing strategies
to inhibit those pathways in the late 1990s to early
and mid-twenty-first century and, since 2006 on treat-
ing the symptoms of degradation.
Progress in understanding degradation pathways for
heritage plastics has been the origin of the data
describing lifetimes. The conservation profession
relied solely on the plastics industry for information
about degradation pathways and rates until the begin-
ning of the twenty-first century when they and
associated stakeholders questioned the frequent mis-
matches. These were likely caused by the use of accel-
erated ageing by industry and the subsequent
extrapolation of those results to real time.
Mesocycles in developing suitable storage microcli-
mates for plastics have mirrored practices for natural
polymeric materials. Initially, actively degrading plas-
tics were placed in isolation and ventilated. In the mid-
1990s, adsorbents designed to remove corrosive vola-
tile materials were used to create specific microclimates
for plastics. Pressure on heritage institutions to be sus-
tainable is increasing the range of low energy
solutions.
The rate of development of interventive conserva-
tion has been controlled by the need to balance the
requirements for reversibility in conservation practices
while retaining original artist’s intent and significance.
Although interventive conservation of plastics is the
newest mesocycle and has only been recognized as
an active area for around 10 years, the range of avail-
able treatments has developed from few, low-technol-
ogy options to innovative, cutting-edge treatments
using nanomaterials.
Because considerable progress has been attained
through multidisciplinary collaborations, such projects
seem promising for the future. Present collaborations
between conservation scientists and environmental
scientists examining the fate of waste plastics in seas
and nanotechnologists formulating drug delivery
vehicles will benefit all parties.
Funding
This work was supported by the European Commission
Horizon 2020 research project NANORESTART [grant
number 646063].
References
Biginagwa, F. J., Mayoma, B., Shashoua, Y., Syberg, K. &
Khan,F.R.2016. First Evidence of Microplastics in the
African Great Lakes: Recovery from Lake Victoria Nile
perch and Nile tilapia. Journal of Great Lakes Re search,
42: 146–149.
Coles, F. 2007. Challenge of Materials? A New Approach to
Collecting Modern Materials at the Science Museum. In: B.
Keneghan & L. Egon, eds. Looking at the Future and
Learning from the Past. London: Archetype, pp. 125–131.
Cózar, A., Sanz-Martín, M., González-Gordillo, M. E., Ubeda, B.
& Gálvez, J. Á. 2015. Plastic Accumulation in the
Mediterranean Sea. PLoS ONE, 10(4): e0121762. doi:10.
1371/journal.pone.0121762
Edwards, H. G. M., Johnson, A. F. & Lewis, I. R. 1993. Raman
Spectroscopic Studies of ‘Pedigree Doll Disease’.Polymer
Degradation and Stability, 41(3): 257–264.
European Union Commission 2003.Green Paper on Environmental
Issues of PVC,http://ec.europa.eu/environment/waste/pvc/pdf/
en.pdf
Fenn, J. 1993. Labelling plastic artefacts. In: D. Grattan, ed. Saving
the Twentieth Century: The Conservation of Modern Materials.
Ottawa: Canadian Conservation Institute, p. 341–350.
Grattan, D. (ed). 1993.Saving the Twentieth Century: The
Conservation of Modern Materials. Ottawa: Canadian
Conservation Institute.
Grzywacz, C. M. & Tennent, N. H. 1994. Pollution Monitoring in
Storage and Display Cabinets: Carbonyl Pollutant Levels in
1
<http:// www.nanorestart.eu>.
Shashoua Mesocycles in conserving plastics
Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-212
Relation to Artifact Deterioration. In: A. Roy & P. Smith, eds.
Preventive Conservation: Practice, Theory and Research.
London: IIC, pp. 164–170.
Kanigel, R. 2010.Faux Real Genuine Leather and 200 Years of
Inspired Fakes. Pennsylvania: Penn Press.
Kopaç, T. & Kocabas¸, S. 2002. Adsorption Equilibrium and
Breakthrough Analysis for Sulfur Dioxide Adsorption on
Silica Gel. Chemical Engineering and Processing: Process
Intensification, 41(3): 223–230.
Laganá, A. & van Oosten, T. B. 2011. Back to Transparency, Back
to Life: Research into the Restoration of Broken Transparent
Unsaturated Polyester and Poly(methyl methacrylate) Works
of Art. In: J. Bridgland, ed. ICOM-CC 16th Triennial
Meeting Lisbon Preprints [CD only].
Michalski, S. 2002. Double the Life forEach Five-Degree Drop, more
than Double the Life for each Halving of Relative Humidity. In:
R. Vontobel, ed. ICOM-CC 13th Triennial Meeting Rio de
Janeiro Preprints. London: James & James, pp. 66–72.
Morgan, J. 1994.A Survey of Plastics in Historical Collections.
London: Plastics Historical Society and The Conservation
Unit, Museums and Galleries Commission.
O’Dwyer, D. 2010. The Contribution of Conservators to
Sustainability at the National Maritime Museum, UK.
Studies in Conservation, 55: 155–158.
van Oosten, T. B. 2011.PUR Facts: Conservation of Polyurethane
Foam in Art and Design. Amsterdam: Amsterdam University
Press and Cultural Heritage Agency of the Netherlands.
Quackenbos, H. M. 1954. Plasticizers in vinyl chloride resins.
Industrial and Engineering Chemistry, 46(6): 1335–1344.
Quye, A. 1999. Care Advice Summary. In: A. Quye and C.
Williamson, eds. Plastics: Collecting and Conserving.
Edinburgh: National Museum of Scotland, pp. 136–137.
Rowbottom, D. J. 2000. Periodization of Training. In: W. E. Garrett
& D. T. Kirkendall, eds. Periodization of Training. Philadelphia:
Lippincott Williams & Wilkins, p. 499–501.
Shashoua, Y. 2003. Effect of Indoor Climate on the Rate and
Degradation Mechanism of Plasticized Poly(vinyl chloride).
Polymer Degradation and Stability, 81(1): 29–36.
Shashoua, Y. 2004.‘Modern Plastics: Do they Suffer from the Cold’.
In: A. Roy & P. Smith, eds. Modern Art, New Museums.
London: IIC, pp. 91–95.
Shashoua, Y. 2005. Storing Plastics in the Cold –more Harm than
Good? In: J. Bridgland, ed. ICOM-CC 14th Triennial Meeting
The Hague Preprints. London: James & James, pp. 358–364.
Shashoua, Y., Schilling, M. & Mazurek, J. 2014. The Effectiveness
of Conservation Adsorbents at Inhibiting Degradation of
Cellulose. In: J. Bridgland, ed. ICOM-CC 17th Triennial
Meeting Melbourne Preprints,Electronic Publication. Paris:
The International Council of Museums, paper 1010.
Shashoua, Y. & Ward, C. 1995. Plastics: Modern Resins with Ageing
Problems. In: M.M. Wright & J.H. Townsend, eds. Resins
Ancient and Modern. Edinburgh: SSCR, pp. 33–37.
Then, E. & Oakley, V. 1993. A Survey of Plastic Objects at the Victoria
and Albert Museum. V&A Conservation Journal,6:11–14.
Ward, C. & Shashoua, Y. 1999. Interventive Conservation
Treatments for Plastics and Rubber Artefacts in the British
Museum. In: J. Bridgland, ed. ICOM-CC 12th Triennial
Meeting Lyon Preprints. London: James & James, pp. 888–893.
Wells, P. Site-Specific Polythene: Experiments in Durability. In: B.
Keneghan & L. Egan, eds. Plastics: Looking at the Future and
Learning from the Past. London: Archetype, pp. 173–178.
Williams, S. R. 2002. Care of Plastics: Malignant Plastics. WA AC
Newsletter, 24(1). http://cool.conservation-us.org/waac/wn/
wn24/wn24–1/wn24-102.html.
Shashoua Mesocycles in conserving plastics
Studies in Conservation 2016 VOL. 61 SUPPLEMENT 2S2-213
