Use of Varnish in Paintings
Originally, the varnish used for the paintings was a resin dissolved in oil. It was used, above all, as a shielding for gold and as a binder of transparent colors. At the beginning of the sixteenth century non-oily varnish was introduced. In a sixteenth-century manuscript of the national library of Florence there is a trace of a "varnish for miniatures", that is a sort of alcohol varnish. The multiple uses of varnish, beyond painting, such as that of waterproofing umbrellas and carriages, open the field of investigation to the possibility that artists have also experimented with less orthodox materials in coloring their paintings.
What is certain is that the painting with varnish was not always performed and many paintings were destined to a representation calmly shiny, or opaque, entrusted only to oil. Some painters used varnish only as a suitable means to remedy the drainage, not for a general treatment of the surface. In the first half of the seventeenth century, various types of varnish are used in the finish of the paintings or as a binder for the painting itself, with the intention of imitating ancient paintings and achieving incredible modulation effects in well-preserved artworks.
A new interest in varnish is brought by the passion for chiaràm, a Chinese varnish that is used for the covering of caskets and objects, very fashionable among amateurs of the late seventeenth century. Being dark and colored, it is certainly not a varnish suitable for paintings, but all the experimentation that goes on around this material between the seventeenth and eighteenth centuries leads to new research and experiments on varnish in general. There are many who sided against the use of varnish for the restoration of paintings.
The problem of varnish lies in the saturation that introduces in the various colors of paintings that were not varnished, also causing imbalances. Masters like Cézanne or Gaugin did not varnish their paintings, and admiring an unvarnished painting is one of the lucky experiences that can happen to someone who loves art. There are varnishings done without improperly saturating the color but also artworks that have been completely unbalanced by varnish. The problem of varnishing presents itself for contemporary art with all its risks, those of improper saturations in works whose message is entrusted to the opaque nature of the surfaces, but also in traditional paintings that cannot be subjected to this operation with impunity.
Varnish, with its yellowing that occurs over time, is presented as one of the means by which we can soften the materiality of a painting. While the fresh paint enhances the light and deepens the dark, the yellowing lowers the clear and lightens the dark, making the set of paintings more homogeneous. There are therefore masters who, beyond the natural alteration of the oil, may have foreseen this effect.