art guide

Conservation and Treatment of Oil Paintings

D. Distortion of original colour

The appearance of the colour of a painted image is subject to the condition of its varnish, old inpainting or retouch and the presence of surface dirt.


  • Discolouration of old varnish : All varnishes discolour with the passage of time, affecting the general colour of oil paint. Oxidation causes some varnishes to become yellow or brown; others tend to become grey. In addition, a varnish may acquire an opacity that flattens the form and reducesontrasts. Some varnishes may "bloom" when they are exposed to excessive humidity.
  • Discoloration of old retouches : Old retouches and inpaintings also tend to discolour with time distorting the painted image.
  • Surface dirt : The regular accumulation of dust on a painted surface is inevitable and often forms a kind of stubborn crust.


The removal of the discoloured varnish and old retouches restores the original appearance of the painting. This treatment requires great sensitivity on the part of the conservator. Preliminary tests must be carried out to determine the solubilities of the varnish and original paint.

Sometimes, grime or discoloured patches simply rest on the topmost surface of a painting; in such cases a conservator might lean the surface without removing the varnish. This can be done by aqueous means or by weak solvents.

fig 1. Cleaning an old, yellowed varnish.
 fig 2 a. Discolouration of old retouches.
 fig 2 b.After cleaning.
 fig 3.Cleaning of embedded grime.
 fig 4 a.Cleaning an old yellowed varnish.
 fig 4 b.After cleaning.