Paintings are usually displayed without the protection of glass, exposed to dust, soot and smoke normally found indoors. Everything that contributes to the soiling of walls also affects the paintings displayed on them. Walls get repainted periodically, yet paintings are left without maintenance for decades.

Old resin varnishes tend to yellow and turn dull with age. A frequent home remedy called for rubbing linseed oil or shellac over the surface of paintings to "rejuvenate" the surface. While this process imparted a fresh sheen, it also trapped all the layers of superficial dirt, smoke and soot and after a few of these treatments, the painting became dark and lost any resemblance to what the artist painted.

Removing these built-up surface coatings, soil and old discolored varnish, reveals the original layers the artist painted, showing colors, that were difficult to suspect under all the dirt.

Cleaning paintings can be very rewarding by permitting us to appreciate and enjoy the artwork the way it was intended by the artist. See the Essay on cleaning.