Cleaning an artwork is a particularly sensitive and demanding part of the conservation and restoration process. The accumulations and deposits of atmospheric pollutants, oxidized varnish, and old restorations, which are likely to distort or darken parts of the work, must be removed.

The aim of cleaning should be in "finding a balance in relation to the whole which, taking into account the present state of the materials can establish as faithful as possible the original unity of the image that the materials have transmitted through time" (Mora e Philippot, 1977:327)

Painted works are usually coated with a layer of varnish. The varnish protects the painting surface from atmospheric deposits. Removal of varnish which has changed color (oxidized) requires thorough cleaning, and is done using a swab and a suitable solvent, only done after an appropriate dissolution test. 

Cleaning should be gradual and systematic, based on progression and taking into account known factors, like a critical understanding of expected results. Cleaning is inextricably linked to the treatment of losses, namely the loss of material the work is comprised of.