Fellows of joys and sorrows, conservators, here is why I am so excited with the recently joined Cleaning workshop: Paper bathing/stain removal, given by Richard Wolbers at the Polytechnic University of Valencia (Spain):
As I introduced in the previous post, the idea is to make every conservation treatment a kind of custom-made dress for each particular object with the advantages mentioned before (I repeat them below) and a minimal initial investment:

• His precepts have a broad spectrum of application, or would I dare to say that they reach any treatment: cleaning of written supports, both bath or locally; and at the same time, deacidification. And paradoxically to this wide ratio, it is in fact a customized treatment to the particular object.
• They can be easily executed and do not require an unaffordable resources investment.
• And the most important: They are soft interventions, very respectful with the artefact and very easily removable, and therefore its innocuousness is almost guaranteed.

To achieve that we will follow the conductivity. This gives us an order of magnitude of the amount of ionic salts. We will measure first the conductivity of the object, and we will use this parameter to build an “à la carte” solution, with a higher, lower or equal osmotic pressure, as appropriate. With these solutions we will module the “eagerness” with which the object will release substances (when we want to clean, with hypotonic solutions) or absorb them (when we want to add, for instance an alkaline buffer during a deacidification; and then we’ll use hypertonic solutions). The goal is to subject the paper to the minimum changes needed to obtain a reasonable improvement, and to do it in the most innocuous way, with weak reactants, easy to rinse and leaving the fewer remnants possible. In order to remove stains locally we would work on isotonic conditions, so that the general repercussion of the treatment would be minor, especially in non affected areas.

Left: Conductivity measurement of a printed paper, with a tiny piece of agarose gel (on the paper). Left: Design of an isotonic solution at a certain pH.

Simultaneously and under the same premise we will adjust the pH. We usually increase pH even when we do not have a precise idea of the value it might achieve at the end. But our customized solution will precisely determine the pH at the end of the treatment and therefore an excess of alkalinity can be avoided. This way the non cellulosic design materials (seizing, inks, glues…) remain unaltered, as well as the insolubilisation of metallic oxides is prevented. We all know how damaging the latter can be and how complex to remove they are.
In order to get this stabilisation of pH Wolbers explains us how to create buffer solutions, adjusting them to the required pH for each particular case and being able to module, at the same time, the conductivity.

Both concepts (pH and conductivity) can be applied to the use of gels, this means that we can design a gel with a particular polarity, conductivity and pH so that it is the most efficient possible for our goal: swell a fatty adhesive, dilute a stain, use enzymes, apply controlled humidity… And at the same time this gel will be the least harmless, because we will control the affected area and how fast will it act. All this without adding to the support any substance that we cannot easily remove.

Gels can be also used as a tool to measure pH, conductivity or even test fugitiveness, locally. Then we can get a previous idea of the effectiveness of a treatment on a negligible tiny spot of the document. Agarose gel is ideal for that: it doesn’t wet, we can reuse it and its neutrality (in pH, conductivity and colour) makes measurement and sample collection very easy.

During the workshop we saw how the use of gels without surfactants (xanthan gel or Velvesil) allow us to work effortlessly combining both properties of two solvents with diverse polarity. With those we can remove stains on papers (left) or either parchment (right), and that can be done in a bath (left) or either in dry cleaning (right) according to the needs of the object.

During the workshop we went deeper in the use of gels and the combination of both polar and non polar solvents to get more effective results than the one we would get separately. Wolbers explains us how cosmetic industry tends to leave aside surfactants to obtain emulsions, using gels instead, much more stable and easy to remove. But that’s not all! Because not only a maximum reversibility is considered, but also non-toxicity and environment-friendlyness is taken into account and this makes it even more attractive, if possible.
The tests with xanthan gel and Velvesil convince us right away. Both allow working in a reasonably large concentration of non polar solvents, but instead of using the common ones (so toxic) we test it with ciclometicone and benzyl alcohol, which turn out to be ideal to swell fatty stains.

Nor in my wildest dreams had I imagined such a close, easy and useful chemistry. Thanks a lot Richard, we owe it to you.

Acknowledgement:

Richard Wolbers for his inspiring ideas, bright explanations and sense of humour. And also to Laura Fuster (Universitat Politècnica de València) for the best of organisations and the translation during the workshop.

Related content:

Latest publications by R. Wolbers:

• Ziraldo, K. Watts, A. Luk, A.F. Lagalante and R.C. Wolbers “The influence of temperature and humidity on swelling and surfactant migration in acrylic emulsion paint films” Studies in Conservation 61(2), in press (2016).

• Lagalante, R.Wolbers,  (2015), “The Cleaning Of Acrylic Paintings.  New Particle-based Water-in-oil Emulsifiers”, CESMAR 7 VII Congresso Internazionale Colore E Conservazione 13-14 Novembre 2015, Politecnico Di Milano, Aula Rogers.

• E. Dillon, A.F. Lagalante and R.C. Wolbers “Aqueous cleaning of acrylic emulsion paint films. The effect of solution pH, conductivity and ionic strength on film swelling and surfactant removal” Studies in Conservation 57(1), 52-62 (2014).

And also some videos:

https://youtu.be/mu7_nS-zF1c?list=PLNks1HQNOQxS8-7_qZPuRQg6NXnymx71M