A technical investigation of an oil painting on copper support, including a study on consolidants for treatment

Paper submitted to e-conservation Journal: Maria Leonor Oliveira, Leslie Carlyle, Sara Fragoso, Isabel Pombo Cardoso and João Coroado, “Investigations into paint delamination and consolidation of an oil painting on copper support”.

This thesis is divided into two parts. Part 1 focuses on the technical study of an undated oil painting on copper. The painting, which depicts the Biblical scene ‘The Visitation’, arrived at the laboratory in poor condition, with severe active flaking which has resulted in extensive paint losses. Part 2 investigates the range of consolidants available to treat flaking paint, and the experiments carried out to determine the suitability of a selection of these. The literature on oil paintings on copper and on consolidants used in their treatment is scarce. Based on the few articles that exist, an empirical pilot study was made of the following synthetic polymers: Paraloid B-67, Paraloid B-44, Regalrez 1094, Paraloid B-72, Mowilith 20, Beva 371b, and Laropal A 81. From these, the last four were selected for a more detailed investigation focused on their interaction with copper, specifically concerning the diffusion of copper ions into the polymeric matrices. This is a topic of interest due to descriptions in the literature of metal particles acting as catalysts in polymer degradation processes. Rutherford Backscattering Spectroscopy (RBS) was chosen to investigate this subject on a series of copper coupons coated with the four polymers. Due to beam damage of the coatings during analysis, the results were inconclusive. SEM/EDS was used to complement the information from RBS, but did not detect the presence of copper in samples from the same films, either indicating that these polymers and copper do not interact; or that the time for the accelerated ageing of the samples was too short. Nonetheless, the material study of the painting in Part 1 successfully established a date range for the painting, and new insights into substances which appear to result from interactions between the copper support and the pictorial layers were found.