The study of the effects of solvents during the removal of varnish from paintings includes two steps: the observation of surface effects by means of the scanning electron microscope and the measure of solvent retention in the paint layer with radioactive tracers. The test samples originate from a painting on canvas of 1895. The varnish removal is carried out following two techniques: with a drop and with a swab. The solvents are classified both according to their degree of strength and according to the length and percentage of retention.