- 1). Create a stable horizontal surface for the painting to rest on while you are working. Cut a piece of cardboard to fit the dimensions of the back of the painting. Place tiles or blocks under the cardboard to reach the height of the painting. Carefully rest the painting on the elevated surface.
- 2). Study the surface to assess the source of discoloration. Use a magnifying glass for a better view. Small dots on the painting may indicate insect excrement, which can be carefully scraped off with a scalpel or removed with a solvent. Smoke, soot and dust can cause a general dirty look, while aged varnish tends to turn yellow over time.
- 3). Assess the surface of the painting. If there are no cracks or chipping paint, attempt a light cleaning with a solution of water and mild soap. Dip a sponge in the solution and test out a small, less obvious area of the painting. If this method removes dirt but does not disturb the paint, carefully continue to clean small areas at a time, using as little water as possible. Make sure that all the soap has been removed.
- 4). Remove the varnish from a painting if it is dirty or yellow. Mix a traditional solution of approximately 50 percent alcohol and 50 percent turpentine. Alternatively, use a newly developed solution to dissolve natural resin varnish, which consists of 60 ml xylene, 12 ml Triton X-100 and 30 ml of a solution of 1-percent Triethanolamine mixed with water.
- 5). Test a 50/50 solution of alcohol and turpentine out on a corner area by applying a small amount of solvent on a cotton swab. If paint is removed along with the varnish, decrease the amount of alcohol or discontinue the cleaning process. Increase the amount of alcohol to remove the varnish, if necessary. Work in small sections while using any solvent, changing swabs. Check the swabs frequently to make sure that paint is not being removed.