In restoration, the operation tends to the removal of dirt from a work of art, through the use of solvents or mechanical means. The cleaning of a painting involves: - the removal of superficial drips and splatters, etc.; - the removal of dirt deposited on the surface and that over time has become partially imbedded in the surface; - the removal of over-painting and altered or disturbing in-painting; - the removal (or better stated, the thinning out) of the altered protective layers (varnishes applied over one another and at times the original varnishes) that inhibit or highly limit the correct reading of the work.