How to remove varnish from an oil painting
However, there may be occasions when you feel you can remove the varnish on your own and the best product to use is Winsor & Newton Distilled Turpentine.
Dammar varnish can be removed using any of our three oil colour solvents: Distilled Turpentine, Artists' White Spirit and Sansodor. It is recommended to use Distilled Turpentine as this has the strongest solvency.
Starting in a corner of the painting, dip a lint free cloth into the turpentine and gently rub the surface of the painting. The varnish should come off onto the cloth - remember to keep a close eye on the cloth and if you see colour coming off then stop. Working in small squares, make your way across the surface of the painting and try to keep using a fresh piece of cloth, as this will help lift the varnish rather than simply spreading it about.