Course review: ‘New Methods in Paper Bathing and Stain Removal’

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.

5 thoughts on “Course review: ‘New Methods in Paper Bathing and Stain Removal’

  1. Thank you for the post. In fact, washing paper with chelating agents has been introduced by CCI (Canadian Conservation Institute) since 1980-ies. It is not anything new. It enables conservator to remove discolourations extremely well, without using bleaches. In Europe somehow this treatment had not been established. Hopefully when Wolbers give such workshops this understanding will spread far and wide. Of course, the treatment needs further research and fine tuning. Hopefully, there would be interest in universities to do this.


  2. I would be most interested to know if you have been able to apply this knowledge in the practical environment of a large institution. Is it possible to simplify the complexity of the subject.


  3. I so far haven’t had many opportunities to, simply due to objects treated and treatment needs.
    I did use this in a professional setting once – treating a series of drypoints with diverse levels of foxing and discolouration. I washed each in a buffered, mildly acidic bath using citric acid as a gentle chelator, then rinsing it out and finishing off with deacidification. Due to lack of equipment/materials I was not able on this occasion to juggle conductivity, but I still found the results satisfying, especially on the foxing.

    In terms of simplifying it, and its use… It might one day be taught as basic paper washing knowledge, which will enhance its use professionally.

    Once the theory is understood, one can take mental shortcuts, provided the correct equipment is available.
    For example, the fact that salts conduct electricity in water and can give you a numerical value to aim for, is already practical with the correct equipment. Casting solutions in gel form is also a good tool to reduce “faffing about”.
    You also can take away what you want out of this – changing conductivity affects fiber swelling, which you may not be concerned with for every object washed.

    Hope this helps!


  4. Hi Anisha. We used citric acid, DTPA, EDTA, and Tiron. Each has different chelating properties/affinities and strengths. We used each under several variations of pH ranges and buffers. Thank you.


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