The cleaning of a paint layer always occurs in two phases. First comes scouring, which consists of removing atmospheric pollution like cigarette, cigar, or pipe smoke, soot, carbon dust, cooking grease, or automobile pollution. In order to accomplish this, we most often use non-ionic, pH-neutral aqueous solutions which allow us to gently remove grime without risk of altering the paint layer.
In spite of everything, this operation can be dangerous in certain cases where water creates blanching on the varnish layer or on the paint layer if it is unvarnished.
Once the paint layer has been cleaned, the varnish layer can be lightened or stripped if it is oxidized and yellowed. This is one of the riskiest steps in painting restoration. Numerous solvents are available, and these are used in mixtures and in different concentrations in order to calculate the effect on the varnish without endangering the original paint layer.
It is sometimes necessary to treat the varnish without using tools. In this case, the restorer must have a sure and experienced touch. Many artworks show glaze, which can be confused with oxidized varnish. A glacis is a transparent, colored layer rich in oil or varnish without much pigment.
The removal or lightening of varnish are operations that can be conducted only with a perfect command of solvents and gestures, as well as an expert understanding of the work, which is why a preliminary study is fundamental.
Exercising care and caution is the rule. A work that has lost its glaze has also lost its physical integrity and its deep nuances – essentially, those qualities which make it a work of art.
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