Testing chelating agents and surfactants for the cleaning of an unvarnished eighteenth century oil painting

Abstract

This study aims at a better understanding of the properties and deterioration of unvarnished paintings together with the possibilities of using surfactants and chelating agents in cleaning systems for their application on an unvarnished eighteenth-century oil painting which is veiled by a whitish layer. Analysis coupled with research indicates this layer to contain lead carboxylates together with deposited calcium carbonate dust. This study presents a methodology of testing various formulated aqueous gel cleaning systems on artificially-aged pre-manufactured replicas, with the aim of developing and adapting a safe cleaning methodology with the least possible testing on the original painting. Complementary analysis of the original fabric and the condition of the painting together with literature study were invaluable for the manufacturing of representative replicas and for the formulating of cleaning systems. Evaluation of cleaning tests was done primarily through optical methods including binocular microscopy (BM) and scanning electron microscopy (SEM) with particular emphasis being given to surface topography, physical and chemical alterations of the paint film and clearance. Results revealed that triammonium citrate (a chelating agent) might be the most efficient cleaning agent with the least damage to the paint layer. The use of Carbopol, which can be thickened to near solidity, is given preference since keeping cleaning action to the surface is a necessity. SEM revealed an efficient clearance of Carbopol mixtures with multiple clearances - either using water and white spirit, or using water and saliva, although further analysis for identification of any organic residues of gelling materials may be needed for confirmation.