Dirt deposition on the paint surface has a tendency to give the painting a grey, dull appearance. Deposits from nicotine usually appear yellowish. Insect droppings on the other hand can react with the paint if left on the surface, irreversibly damaging the paint.
The cleaning of a painting is a delicate and complex process that should only be carried out by a trained painting restorer after testing and careful examination of the work of art.
Generally, aqueous cleaning systems are very effective at dirt removal. However, especially with modern and contemporary paintings certain paints and pigments may be sensitive to moisture. The sensitivity can be lowered by modifying the pH and conductivity of the water, to match that of the to be cleaned surface.
Further modifications may include the addition of surfactants or detergents, as well as chelating agents, to allow a better solubilization of the dirt. Aqueous cleaning solutions may also be gelled, allowing greater contact time between the cleaning solution and the surface to be cleaned.
Oil painting during surface cleaning