8. Recommendations for further work
The results of these analyses indicate that DEAE and its reaction products are present on some paintings. Some of the effects attributed to DEAE contamination may be due to the presence of water soluble components like starch or protein (glue, egg, etc.). Since the number of paintings examined for this report is so small, a true picture of the extent of the DEAE problem cannot be drawn. More paintings should be analyzed.
FTIR microspectroscopy is the quickest, most informative, and least intrusive technique to use for this analysis.
To clarify the extent of the effects of DEAE and the mechanism of its interaction with painting the following further work is recommended:
- Minuscule samples should be taken of varnishes and paints from many paintings that are apparently subject to DEAE contamination problems, for analysis by FTIR microspectroscopy, specifically for the presence DEAE esters and DEAE carboxylates, and for the presence of water soluble or water sensitive materials like starch and protein. This should quantify the number of paintings that are affected by DEAE and the extent of the DEAE problem.
- Test samples or model paintings should be exposed to DEAE vapors then analyzed by FTIR microspectroscopy to clarify the chemical reactions between painting media, DEAE, and DEAE reaction products. This has already been done to some extent in developing the FTIR microspectroscopic analysis procedure. The additional work needs to use more realistic exposure conditions such as exposure to a DEAE/air mixture of about 1% DEAE, rather than pure DEAE vapors or immersion in liquid DEAE. This would determine whether the interactions under less severe exposure conditions are the same as at the higher concentrations used in the FTIR analysis.
- Test samples or model paintings should be analyzed by microscopical methods, before and after exposure to DEAE, and before and after cleaning treatments to determine the physical or structural effects of DEAE exposure and subsequent cleaning of DEAE exposed paintings.
- The analysis reported here has shown that for some paintings, wiping with water moistened swabs removes water soluble compounds from the painting, including starch and protein (“Ste. Catherine”) and DEAE reaction products (“Green Trees”). Additional tests should be made to determine if swabbing with water moistened swabs is an effective treatment for removal of DEAE reaction products. DEAE reaction products are polar compounds and therefore soluble in polar solvents like water and alcohols. They are also surface active agents and therefore may be soluble in nonpolar solvents like aliphatic and low aromatic hydrocarbons such as mineral spirits or naphtha. Alkanolamine soaps such as those produced by reaction of monoethanolamine (MEA) with coconut or tall oil fatty acids show some solubility in these solvents. Analogous DEAE soaps with the increased hydrocarbon content due to substitution of the two hydrogens on the nitrogen of MEA by two ethyl groups will be even more soluble in these solvents. The effects of using these solvents to remove DEAE reaction products should be investigated. Using nonpolar solvents that may be less damaging to paintings than water, may be a valuable alternative.