A comparative study of the effect of cleaning treatments on historic papers

Abstract

Paper conservation science is a field that emerged in response to the necessity for the understanding of the scientific basis of treatments used by paper conservators/restorers. This study deals with an investigation of the effects of eight wet-cleaning treatments, namely immersion washing in three different water sources (tap water, deionised water and distilled water), simple chemical treatments involving bleaching with a 153 hydrogen peroxide solution or deacidification in a 23 solution of calcium hydroxide, as well as combinations of these two chemical treatments, on an 18th century and a late 19th-century paper. When carrying out chemical treatments, the papers were also washed by immersing in tap water, both prior and post treatment. The effect of the cleaning treatments on five different properties, namely colourimetric properties (CIE L*a*b* coordinates), crystallinity index (X-Ray diffraction), pH (cold-extraction method), degree of polymerisation (viscometry), and carbonyl content (modified Szabloc Methodology), were investigated. It was determined that all cleaning treatments affected the colourimetric properties of the two sheets. However, the degree of crystallinity and polymerisation were not found to differ upon cleaning. Carbonyl content and pH varied to different degrees depending on the treatment used. It is also interesting to note that the 19th-century paper was found to be more chemically degraded than the 18th century paper. This is perhaps observed in later papers due to the lower quality raw material being used as the demand for paper increased. From the immersion washing treatments, it was observed that immersion washing in tap water gave the lowest levels of change. However, when washing with distilled or deionised waters, the carbonyl content was observed to increase. This points towards the unsuitability of using these purified sources when washing. As expected, the simple chemical treatments, deacidification and bleaching, affected different properties to different extents. However, when combining them, it was determined that possibly deacidification prior and post bleaching is the most suitable method for use since it limits oxidative damage caused by the hydrogen peroxide bleach used while also neutralising the acidity produced. Thus, this study has shown that the general practice of using tap water for washing may in fact provide benefits to the papers treated. Also, bleaching is ideally combined with deacidification steps both before and after the bleaching stage. Furthermore, various correlations were observed, showing that as the carbonyl content and acidity levels increased (indicating degradation) colourimetric coordinates shifted away from neutral colouration, suggesting that colourimetry may be used to infer changes in other properties. This is of essence since colourimetry is a non-invasive technique whilst the current methods for studying other properties involve destructive techniques, a situation to be avoided as much as possible in conservation.