Greener solvents for conservation

Problem statement

Art conservators must often rely on organic solvents for the cleaning, coating and protecting of art works. Organic solvents are volatile, flammable and often toxic for humans and aquatic life. Since conservators sometimes work in studios, without air evacuation, it is really important to protect the protectors of our cultural heritage. The aim of this project is adapting organic solvent use so less toxic solvents – with similar or better performance – find their way to conservation practice. 

Research question

Can we replace harmful organic solvents with sustainable alternative solvents in the conservation of cultural heritage?

• We are searching for green solvents for preparing varnishes based on four commonly used resins in various restoration practices: Dammar, Paraloid B72, Laropal A81, and Regalrez 1091.
• Do the green solvents meet the requirements of good restoration practices?
• Do the cured varnish films meet the requirements of good restoration practices, and are the mechanical properties of these films comparable to or better than the state-of-the-art?

Research approach

We develop an approach to selecting and testing alternative solvents that are less harmful to humans and the environment, while maintaining professional considerations based on the requirements of the individual artwork. For determining potential greener solvents, the selection criteria are based on: Hansen solubility parameters and the intended solubility of the resins Dammar, Paraloid B72, Laropal A81 and Regalrez 1091 plus the rubber Kraton g (additive); important physical properties of the solvents and solvent mixtures typically used for their application; and specific safety, health and environmental risk limits. 

The SUSSOL-software (sustainable solvent selection and substitution software) is used, which uses an artificial neural network to cluster solvents based on their physical properties. More sustainable solvents are proposed, from which varnish solutions are prepared using the above-mentioned resins. Initial practical testing of these is carried out on standardised canvas boards, from which a subset is selected for varnish testing on a historical painting that was donated for testing. Similar 'control' varnish solutions of the above resins (with traditionally widely used solvents) are prepared and tested in the same way. The workability for their brush application and the aesthetic qualities of the different varnish solutions are then compared on the historical surface according to professional requirements. Casting films and samples on white canvas boards (with controlled application) are prepared for standardised coating tests, including scratch hardness tests, water resistance, gloss and colour measurements.

Output

From this study various safer (greener) substitute solvent and mixtures will be suggested for the above resins when applied as varnish coatings on paintings, with an approach that further successfully acknowledges the individuality of a painting surface for informing specific testing and selection.

With this we further prove the applicability of SUSSOL in various domains.

The results are disseminated through a scientific publication (technical note) in a conservation oriented journal. This technical note will be supported by a full paper in a more multidisciplinary journal to emphasize the importance of cross-disciplinary research. Through close collaboration with SiC, SRAL and the Horizon project Go Green, the good practices developed in this project will find their way to conservators around the world.