Paper Conservation: Decisions & Compromises

Verdigris I: Compromises in Conservation
Christa Hofmann | Andreas Hartl | Kyujin Ahn | Laura Völkel | Ina Faerber |
Antje Potthast
Austrian National Library, Conservation Department, Vienna, Austria
University of Natural Resources and Life Sciences, Department of Chemistry, Vienna, Austria
Fig. 1: Kyeser, Bellifortis, mid 15 th century, Cod. 3068
Fig. 2: Cellarius, Atlas Coelesti sue Harmonica Macrocosmica,
1708, FKB 272-25.
Copper green pigments have the potential to
cause severe degradation of paper and parchment.
Additives, application method and storage conditions
influence the visual appearance and chemical
stability of the colour. At the Austrian National
Library manuscripts, prints and maps coloured
with verdigris display different stages of degradation
(Fig. 1, 2). Finding stabilising conservation
methods and providing conservators with
decision making tools was the aim of a research
project funded by the forMuse programme of the
Austrian Ministry of Science and Research.
Samples were prepared by applying copper acetate
pigments mixed with gum arabic on hand
made rag paper sized with gelatine. After preaging,
the first group of samples was subjected to
treatments with a variety of solutions including
aqueous deacidification, non aqueous de-acidification,
antioxidants and complexing agents.
The solutions were applied by air-brush on the
suction table or by brush on the verso. The second
group of samples received an application
of coated Japanese tissue papers for mechanical
reinforcement. For the purpose of comparison
the coated tissue papers were also adhered on
rag paper without colour and on Whatman No.
1 filter paper. The coating agents ranged from
aqueous to non- aqueous adhesives, and could
be activated by water, ethanol or heat. A third
group of samples was prepared according to
historic references and recipes by the mixture of
verdigris with plant dyes, pigments or juices. After
preparation and treatment, the three groups
of samples were light- and heat-aged.
The effect of the solutions on cellulose was evaluated
by analysis of molar mass and carbonyl
group content before and after aging. The coated
Japanese tissue papers were visually assessed and
submitted to simple mechanical testing. Indicator
papers were used to monitor migration of
copper ions during treatments. LA-ICP-MS (Laser
Ablation-Inductively Coupled Plasma-Mass Spectrometry)
was performed on selected samples to
further evaluate the movements of copper ions.
The verdigris samples with different additives
were visually compared before and after aging
with green colours found in manuscripts, early
printed books and maps.
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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