What could occur if oil paint is varnished too early?

Using varnish on oil paint too early can lead to the paint remaining tacky and not drying properly. This is primarily due to the fact that oil paint undergoes a drying process that involves oxidation, which can take a significant amount of time, sometimes weeks or months, depending on various factors such as the thickness of the paint and the environment.

When varnish is applied prematurely, it creates a seal that traps solvents and moisture within the paint layer. Since these solvents cannot evaporate, they result in a sticky surface that prevents the oil paint from curing completely. The trapped solvents can also lead to issues such as discoloration or a change in the texture of the paint over time.

In contrast, once the paint has fully dried and cured, applying varnish can protect the artwork and enhance its colors without creating such complications. It plays a role in sealing the paint to prevent dust accumulation and to further protect against environmental damage, but this can only happen after the oil paint is completely dry.