Cleaning a picture can involve the removal of dirt, grime or accretions that have built up over time on the surface of the work of art (or, as in the case of the blue contemporary artwork on the right, splashes of Coca-Cola). The cleaning of a painting is a delicate process that should only be carried out by a trained picture restorer after testing and careful examination of the work of art.

It is crucial that dirt is removed from paintings as this dirt can carry materials that will stain unprotected paint surfaces. Dirty paintings are generally cleaned using an aqueous solution.

Dirt on contemporary un-varnished surfaces requires a dry cleaning method.