Paper Conservation: Decisions & Compromises

Solutions that have the potential to chemically
stabilise verdigris on paper (Ahn, Verdigris II)
need to penetrate the paper matrix. In this study
the solutions had to be applied by brush in order
to have a positive effect on cellulose. Spraying of
solutions on the suction table minimised migration
of copper ions during treatment. The movements
of copper ions could be monitored with
indicator papers. The visual observations were
confirmed by LA-ICP-MS. Treatment decisions
will be a compromise between the risks of migration,
the change of media and possible beneficial
effects of applied solutions. High humidity during
storage and treatment can lead to migration
of copper ions and enhance degradation of cellulose.
For mechanical stabilisation of paper degraded
by copper green pigments, Japanese papers
coated with films of adhesive offer the possibility
to support the weakened paper carrier. By
using thin and matte adhesive films produced
on a silicon mat, in combination with tissue
papers, 2 -3.7g/m 2 , the visual interference can be
reduced. Activation of the adhesive coating with
the sponge-blotter-system developed by Jacobi
(Jacobi et al. 2011), minimises the risk of migration
of copper ions. In this study, coatings with
wheat-starch paste-methylcellulose, gelatine and
Klucel G in ethanol proved to provide sufficient
strength without leading to detrimental effects
on the mechanical and visual properties. The use
of a specific adhesive or adhesive mixture can be
adjusted to the needs of an artefact. Conservators
have a range of options to find the best compromise
between strength, visual appearance, ease
of application and removal.
Verdigris seems to have been frequently applied
in mixtures with green and yellow plant colours
to produce different shades of green (Fig. 1). The
exposure to light represents a risk for these light
sensitive compositions. Light seems to play a role
in initiating degradation of cellulose in the presence
of copper acetate. Plant colours and additives
like vinegar, tartaric acid or alum can lead
to brown discolorations during aging. The quality
of paper, sizing, method of colour application
and environmental factors influence the condition
of verdigris. Liquid application of colour,
high humidity during storage and the direct
effect of water have a negative impact. Treatment
decisions will have to balance the previous condition
and history of an artefact with the sideeffects
of an intervention.
The conservation and preservation of verdigris
on paper will, in most cases, be the search for
an acceptable compromise: between penetration
of solutions and migration of copper ions, between
the support of degraded paper and visual
change, between the complexity of the artefact
and the question of access.
Acknowledgements
The authors thank their project partners
at the Conservation Department of the
Austrian State Archive, the Preservation
Directorate of Library of Congress and
the University of Natural Resources and
Life Sciences. The project was funded by
the forMuse programme of the Austrian
Ministry of Science and Research.
Authors
Christa Hofmann 1 | Andreas Hartl 1 |
Kyujin Ahn 2 | Laura Völkel 1 |
Ina Faerber 1 | Antje Potthast 2
1 Austrian National Library, Conservation
Department, Josefsplatz 1,
1015 Vienna, Austria
christa.hofmann@onb.ac.at
2 University of Natural Resources and Life
Sciences, Department of Chemistry, Muthgasse
18, 1190 Vienna, Austria
antje.potthast@boku.ac.at
Reference
Jacobi, E., Reissland, B., Phan C., Luu T.,
van Velzen B. und Ligterink F. 2011. „Rendering
the Invisible Visible: Preventing
Solvent-induced Migration During Local
Repairs on Iron Gall Ink”. Journal of Paper
Conservation 12 (2): 25-38.
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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