Preliminary study into the reduction and removal of naturally aged varnishes from painted surfaces using an Er:YAG laser in a two-step cleaning process with solvents

Abstract

A preliminary study into the reduction and removal of naturally aged varnishes, aimed at collating observations to encourage further study of the cleaning of paintings with intractable, difficult to remove coatings, is presented in this article. Er:YAG laser cleaning trials with dry laser exposures followed by solvent removal of natural resin varnishes were conducted on a naturally aged test panel, and an expendable nineteenth-century oil painting. Surfaces were examined with normal and ultraviolet light, a headband magnifier, and low-power digital microscopy, videography and colorimetry. Standard solvent cleaning tests were first carried out, followed by a two-step cleaning protocol where Er:YAG irradiation of the coating was followed by solvent cleaning, the laser being used to promote a weakening or disaggregation of the topmost portion of the layer or layers of varnish. The aim was to assess the laser cleaning outcomes conservators might expect on ‘real’ as well as mocked-up surfaces; results are presented from one of each. Cleaned areas of paint were also directly exposed to Er:YAG irradiation to determine a safe fluence with observations limited to relatively low magnifications. Overall these efforts inform the risks and contribute to the development and the safe use of this novel cleaning method.