Rubbing varnishes are so made that they may take a “rubbed finish.”
Varnishing should be done in a room in which the temperature can be kept from 70 to 80 degrees Fahr., and which is comparatively free from dust. The surface to be covered must be clean, dry and filled even and smooth.
155. Shellac.
—Shellac or spirit varnish is a solution of lac and alcohol. Lac is soluble in both grain and wood alcohol but grain alcohol is preferable. Beds of crude lac are found in parts of Africa and South America where the lac has been left by the decay of leaves and twigs which it at one time encrusted. Crude lac is deposited upon leaves and twigs of certain of the lac-bearing trees by countless numbers of insects which draw out the sap.
Stick-lac is crude lac which has been purified somewhat of the bodies and eggs of the insects and rolled into stick forms. When crushed and washed it is known as seed-lac. When fully purified, which is done by melting and straining, it is spread out and is known as shellac.
White shellac is obtained by bleaching. Orange shellac is unbleached. Pure white shellac is used where the more yellow shellac would discolor. Orange shellac is stronger than white and will last longer but is harder to apply because it sets more rapidly.
Shellac varnish sets quickly, dries hard but softens under moisture. Unlike oil varnish, it does not “level up” and must, therefore, be brushed on quickly, using long, even strokes. No spots must be omitted for they cannot be “touched up.”
156. Shellac Finishes.
—The use of one or more coats of shellac preparatory to a varnish finish has been noted.
A very simple finish, and one that is easily applied, is obtained by covering stained wood with a very thin coat of shellac.