The Painter in oil

Varnishes. - When the picture is done, varnishes are used to bring out the freshness
of color, and to preserve the surface from outside influences of all sorts. A picture must
be well dried before it is varnished, or it is likely to crack; six months is not too long to be
safe. If you are in a hurry to varnish, use a temporary or retouching varnish.
The best varnish is necessary for use on pictures. Never used any except a varnish
especially made for the purpose by a reliable colorman. Those made by Winsor and
Newton may be all depended upon. Pay a good price for it, and don’t use too much.
Mastic varnish is that which is most favorably known. Be sure you get a good and pure
quality.
Varnishes are made from various gums or resins dissolved in a solvent such as alcohol,
turpentine, or oil, as the case may be. The latter gums are the best for pictures, because
they do not affect the color of the picture. Much care should be used in putting on the
varnish - that it is even and as thinly distributed as will serve the purpose. It should not
be flowed on, but carefully worked out with a clean brush, and then kept from dirt and
dust until dry.
The finer varnishes in oil or turpentine are best for ordinary use. Those in alcohol do
not hold their freshness so well.
Varnishes are sometimes used as siccatives, and to mix with colors which are liable to
affect other colors, but to lack consistency. Usually, however, they are not needed.