Camille PolkownikÉcole nationale supérieure des arts visuels de La Cambre (Brussels)Painting conservation - contact details: camille.polkownik@hotmail.fr

Replacing the TEA in resin and bile soaps

Natural Resins Removal These soaps are used to remove natural varnishes (affinity between the molecular

structure of the acids and the natural resins). They can be used as an alternative cleaning method,

when traditional cleaning systems (solvents) fail. They function especially well on

oxidized varnishes that solvents cannot remove without sensitizing the paint layer; dusty varnishes;

or when there is an oily component in the varnish layer.

TEA: A Problematic Ingredient? Studies done in the 1990s gave worrying conclusions on the uses of soaps, especially

concerning the residues. But looking closely, one will realize the studies used high pHs soaps

(Erhardt and Bischoff, 1994), large amounts of TEA (Erhardt and Bischoff, 1994) or an inadequate

rinsing method (Koller, 1990). All these elements will raise the leaching levels, and the quantity

of residues and will thus induce optical/physical/mechanical changes. Even if it is difficult to draw

precise conclusions from such studies, a couple others were realized respecting pH parameters,

original recipes and appropriate rinsing method (Ford and Byrne, 1991). One ingredient is pointed

out: triethanolamine. One thing we are sure of is its poor ageing: it becomes yellow/brown

upon light and air, which is very problematic if there are indeed residues left after cleaning/

rinsing.

Replacing the TEA In order to replace the TEA and still have an active mixture, it is important to be acquainted

with its properties and functions in order to choose matching components. The TEA combines

solvent action (from the alcohol), chemical action (it acts as a base - amine), chelating action

and emulsifying action. Plus, the pKa is 7,8 which enables a buffer solution with a pH to be made

around 8 (knowing the painting cleaning security range is between pH 5,5 and 8,5).

It is important to choose ingredients that will age well and which are easily available to conservators

and of analytical quality (via Sigma Aldrich for example).

The following components were chosen: pKa Supplier

Tris Base 8 SigmaBis Tris 6,5 SigmaEthomeen C25 7 SigmaDi sodium tetraborate 9,5 UnknownSodium hydroxide 13 UnknownPotassium hydroxide 13,5 UnknownAmmonia 9,2 Unknown

For this study, 87 soaps were prepared, with/without different additives

(benzyl alcohol, Surfonic JL-80X) and different pH (fig. 3). TEA soaps were also made in order to

compare their efficacy with the new soaps. Given the low budget of this present study (conducted

while the author was a Masters student), the samples could not be observed via SEM or with

radioisotopes. A fluorescent tracer (fluorescein) was added in hope to make the residues fluoresce

under U.V. light (fig. 4), and under different magnifications (X 50 to X 500). No residues could be

observed under these conditions, but it is most likely the analytic technique used here was not

optimum for this purpose.

Thus, the study focuses on the efficacy of the new tailored soaps on different varnish

layers. The soaps were tested on 20 paintings in the La Cambre Painting Conservation Studio: only

the most striking treatments are presented in this poster. Both paintings (figs. 5 to 10) presented

bits of oxidized varnish left after solvent cleaning, leftovers that could not be removed with solvents

without sensitizing the paint layer. Moreover, the second case (figs. 8 to 10) had dirt embedded

in the varnish, making the solvent action ineffective and damaging the paint layer at the same

time. Both paintings were successfully cleaned with the « new » resin and bile soaps, with and

without additives.

ConclusionsAfter testing the soaps on many varnish layers that were problematic (could not be cleaned with solvents due to high oxidization, grime embedded in the layer, small oil content...), the following conclusions could be drawn:

• Soaps without additives were slow acting. Adding solvent and/or surfactant enhanced the action, but only for the soaps that were effective in the first place. The additives act as a « booster » to the mixture.

• Soaps with Tris Base and disodium tetraborate were the most effective, as much or more than the TEA based soaps.

• Soaps with Bis Tris and Ethomeen C25 were slower, even with the additives. They usually could not dissolve the varnish layer entirely. This may be due to the low pH of these mixtures (7,5 for both, due to low pKas).

• Soaps with sodium hydroxide, potassium hydroxide and ammonia were ineffective and somehow difficult to make due to their high pKas.

• It is possible to replace TEA in the resin and bile soaps but to do so, the working mechanism, the functions and the proportions of the components must be perfectly understood.

Outlook: even though the efficacy of these new soaps is encouraging, more work needs to be done on the potential residues left by these new products.

Fig. 1: Triethanolammonium abietate salt.

Fig. 2: Triethanolammonium deoxycholtate salt.

Figs. 6 & 7: Before and after cleaning oxdized varnish fragments with disodium tetraborate/deoxycholic acid soap (pH 8,5). Additives in the soap: benzyl alcohol (3 %) and Surfonic JL-80X (1 %).

Fig. 3: New tailored soaps (87).

Fig. 4: Soaps under U.V. light.

Figs. 9 & 10: Before and after cleaning, showing oxidised varnish fragments embedded with grime, with Tris Base/abietic acid soap (pH 8,5), no additives.

Fig. 5: L‘amateur, D. Ryckaert, 17e, Musée des

Beaux de Liège (BE).

Fig. 8: Portrait du Bourgmestre Maigret, Lamet, 1743,

Musées de Verviers (BE).

What are resin and bile soaps? Bile soap is a salt made from the reaction between deoxycholic acid and triethanolamine

(TEA) in water (fig. 1). Resin soap is a salt made from the reaction of abietic acid and TEA in

water (fig. 2). The resulting solution can receive additives such as solvent, surfactant, chelating

agents...before gelation with a cellulose ether. Since all the components except water

are non-volatile, it is essential to perform a thorough rinse (water then hydrocarbon-based

solvents) to avoid residues. These products were invented by Richard Wolbers in the 1980s and

were introduced to conservators at the ICC Congress held in Brussels in 1990.

This poster is a summary of the Master Thesis: « Wolbers’ Bile and Resin soaps ; Replacing the triethanolamine », presented in June 2014 at La Cambre, Brussels, Belgium.

List of IllustrationsFig. 1: triethanolammonium abietate salt.Fig. 2: triethanolammonium deoxycholate salt.Fig. 3: tailored soaps (87), picture by the author.Fig. 4: soaps under U.V. light, picture by the author.Fig. 5: L‘amateur, D. Ryckaert, 17e, Liège Museum (BE), picture by Ms. Militza Ganeva.Figs. 6 & 7: Before and after cleaning, showing owidised varnish fragments embedded with grime, with disodium tetraborate/deoxycholic acid soap (pH 8,5), pictures by the author.Fig. 8: Portrait du Bourgmestre Maigret, Lamet, 1743, Musées de Verviers (BE), picture by Ms. Jade Roumi.Figs. 9 & 10: Before and after cleaning oxidized and grime embedded varnish bits with Tris Base/abietic acid soap (pH 8,5), pictures by Ms. Jade Roumi.

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