The effects of plant dyes, watercolours and acrylic paints on the physical, chemical and biological stability of Japanese tissue paper used in paper conservation

Abstract

Despite substantial literature on the dyeing of textiles, there is a lack of research about dyeing and colouring Japanese mending papers for paper conservation purposes. In this study, a range of scientific techniques have been applied to improve understanding of the physical, chemical and biological properties of Japanese mending papers after treatment with various dyes and pigments. A variety of toning materials including plant dyes, watercolours, acrylic paints, inks, pastels, gouaches, and colour pencils are commonly used by conservators for paper toning purposes. Plant dyes are often used in artisanal practices including painting, handicrafts, textiles and paper dyeing; however, the chemistry of such colourants and their interaction with Japanese mending papers used in paper conservation has not been studied. The basic premise of this study is that a conservation treatment should not contribute to the physical, chemical or biological degradation of mending papers used for paper conservation purposes and should, ideally, prevent such degradation. In this study, two Japanese tissue papers (Yukyu-shi and Sekishu Mare) were treated with selected plant dyes, watercolours and acrylic paints. Paper specimens were subject to both moist-heat artificial ageing and accelerated photoageing and colour changes were measured using spectrophotometry and microfading tests (MFTs). Physical experiments (folding endurance, tear resistance) and chemical tests (pH) were used to investigate the paper degradation mechanisms to achieve a better understanding of how paper deteriorates as a result of artificial ageing. The results show that, in general, the papers treated with plant dyes are more acidic than those treated with watercolours and acrylic paints. Almost all of the plant dyes tested in this work showed some degree of fading as measured by spectrophotometry, compared to untreated controls and those samples treated with watercolours and acrylic paints. By contrast, synthetic artists’ pigments were relatively stable to colour change. Acrylic paints and watercolours are the most widespread colourants used by paper conservators and their continued use over plant dyes is justified by this study. While their use is undergoing a revival and they are seen to have heritage value as a traditional product, plant dyes may not be suitable for colour-matching the retouched parts of ancient books and documents because of their propensity for colour change over time. Dyed papers also displayed less folding and tear resistance after ageing and there was a difference in these properties between Yukyu-shi and Sekishu papers. The untreated Sekishu papers and the Sekishu papers treated with watercolours and acrylic paints exhibited greater tear resistance than the Yukyu-shi papers. The Sekishu and Yukyu-shi papers in untreated form and when treated with acrylic paints, as well as the Yukyu-shi papers treated with plant dyes, demonstrate effective folding endurance after ageing. A further aim of this thesis was to quantify the growth of Aspegillus niger and Penicillium rubrum fungal species on Japanese tissue papers with the aid of real time polymerase chain reactions (PCR). This technique amplifies deoxyribonucleic acid (DNA) from the target species which is a proxy for species abundance. Universal PCR primers amplified DNA from both A. niger and P. rubrum and these species were found to grow preferentially on Yukyu-shi paper, regardless of the treatment. Sekishu papers treated with most plant dyes and chemical colourants were more resistant to fungal growth than similarly treated Yukyu-shi papers. In summary, this study suggests that for the best long term preservation outcomes for paper materials in archives, libraries, galleries and museums, acrylic artist paints generally perform better in conservation terms than plant dyes and watercolours. This must be balanced against the fact that traditional paper conservation practices may have particular cultural values in some circumstances. Important new insights and opportunities to improve conservation outcomes, and safeguard unique cultural heritage, can be based on the innovative use of an array of scientific techniques that question established cannons.

Date of Award	2015
Original language	English
Supervisor	Tracy IRELAND (Supervisor) & Dennis Mcnevin (Supervisor)