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Why are synthetic resins used as varnishes on some paintings?

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Inside the ongoing preservation of the Vatican — Art conservation and restoration Learn about the restoration of tiles in St. Peter's Basilica, Vatican City.

Synthetic resins are widely used as varnishes in art conservation because they offer superior chemical stability compared to traditional natural resins like mastic and damar.1

While natural resins are valued for their aesthetic qualities, they tend to become brittle, yellow, and less soluble as they age, making their eventual removal difficult and potentially harmful to the painting. In contrast, synthetic resins are specifically chosen for the following reasons:1

Chemical Stability: They are resistant to deterioration from light and atmospheric conditions, ensuring they do not rapidly discolor or physically degrade.1
Reversibility: They are formulated to remain soluble, allowing conservators to remove them safely using appropriate solvents during future treatments.1

Commonly used synthetic options since the 1960s include acrylic copolymers and polycyclohexanones. Conservators continue to research new formulations, such as hydrogenated hydrocarbon styrene and methyl styrene resins, to better balance ease of application, long-term stability, and the desired aesthetic appearance.1