Last year, I had the pleasure of attending Richard Wolbers’ three-day workshop ‘New Methods in Paper Bathing and Stain Removal’. We were introduced to several concepts that form the basis of a systematic approach to bathing paper that ‘manages’ water and effectively tailors a bath to the object being treated.

The nature of paper, specifically its organic fibre base, makes it an extremely water-absorbent material that is affected by osmosis. Over the first half of the course, we were taught how to change the chemistry of water to match a paper’s intrinsic salt content, thus controlling osmotic pressure. Because salts conduct electricity, we could calculate the salt content of a piece of paper by measuring its conductivity, which enabled us to prepare a water bath with a conductivity that matched that of the paper.

Fig. 1: Wash waters with different chelating agents and pH lined up for comparison. ©Mathilde Renauld

Another way of adapting water is to change its pH. Richard suggested that within the range of pH 5 to 6.5, pH changes do not affect fibre swelling, and thus he recommended washing in this range. He advised that a pH above 8.5 was a dangerous range at which to work, as this level of alkalinity promotes the formation of metal hydroxides: metal ions which exist within the paper structure find themselves bonded to OH groups, in which form they are nearly impossible to extract with standard chelating agents.

Richard also promoted changing the chemistry of water by adding chelators to routine wash treatments, as metal ions are present in most papers as a result of the manufacturing process. We carried out a comparison of four different chelating agents at different pH levels, on papers from the same source sample. We then compared the wash water of each bath, and indeed each came out a different colour, despite the concentrations, conductivity and washing time all having been held constant (Fig. 1). This highlights that not all wash waters are suited to all papers and that chelators can help improve the effectiveness of the washing.

To make things practical, Richard has devised a method to locally test which solution is best adapted to which paper object. If each solution is cast into agarose gel, a small portion of the gel can be left to act on the paper, which will indicate which solution is the most effective (Fig. 2). We all got to go home with a ‘test kit’ of the solutions we made, in gel form, during the workshop.

Fig. 2: Small gel plugs of each solution, after having been left overnight. The white spots indicate the effectiveness of the varying solution strengths used on this particular paper. ©Mathilde Renauld

I am truly grateful to have received financial support from the York Foundation for Conservation and Craftsmanship for attending this workshop.

Mathilde Renauld is a recent graduate from Camberwell College, London and is now Project Conservator at The National Archives. Her undergraduate degree was an MA (Hons) in History of Art at Glasgow University, during which she studied for the first two years of a Chemistry MSci and developed an interest in paper conservation.