Continuing the discussion over the cleaned pictures in the National Gallery, London (see IIC Abstracts, 3822 3840, etc.) the author argues that some painters anticipated the effects of time by exaggerating some colours which they knew would tone down. Evidence is cited from Diderot, Vernet, Renoir and others in support of this theory. It is alsopointed out that it is an often-repeated fallacy that paint on top of the varnish must always be a later addition. In the Renaissance it was the exception for varnish to be applied over the whole area of the picture. After the sixteenth century it was customary to use varnish for glazes, while the idea of varnish as a uniform surface coating did not occur before the middle of the seventeenth century.