Artwork conservation materials and Hansen solubility parameters: A novel methodology towards critical solvent selection

In research and in actual conservation practice, conservators have to choose adequate methodologies for carrying out treatments successfully, while respecting the integrity of artworks. Besides the knowledge of the authentic materials present in each artwork, conservators must be able to choose appropriate conservation materials and methods. Solvents are widely used in cleaning, but solubility issues are also of high importance in consolidation treatments as well as in protective coating applications. The central aim of this work is to critically re-assess the potential of Hansen solubility parameters (HSPs) for a reliable use in the field of artwork conservation. An effort was made to develop an efficient methodology for critical solvent selection (CSS). For this purpose, two different methods were used for the estimation of various artwork conservation materials. A group-contribution method (GC), based on the chemical composition of materials, was applied for the prediction of HSPs of egg yolk, pine resin and seven red organic colorants (Mexican, Polish and Armenian cochineal, kermes, madder, lac dye and dragon's blood), traditionally used in paintings, textiles and illuminated manuscripts. Additionally, an experimental set up was used for testing the solubility of the commercial products of synthetic conservation materials, Primal AC-532K, Beva gel 371 a and b (old and new formula) and a commercial matt varnish made of dammar and wax. With the direct use of Hansen solubility parameters and the relative energy difference (RED) between various materials it was made possible to carry out ad hoc “virtual” solubility tests that may apply to real and complex systems such as cultural heritage artworks.