For exterior work a special exterior varnish should always be specified. Exterior varnishes are also known as spar varnishes, because largely used for coating the spars and exposed woodwork of ships. They are higher in price than the corresponding grades of interior var nish, because it is necessary to use the harder and more expensive copals in their manufac ture. Although the gums used are hard, ex terior varnishes must dry with more elasticity than is necessary for interior varnishes, since they must stand greater changes of temperature.
Interior varnishes are of two classes—those that are adapted for rubbing to a dead surface or to a polish, and those which cannot be rubbed but will roll up under the action of the pumice stone. Left in their natural gloss, these latter varnishes would remain in good condition as long as a rubbing varnish. When a dead surface is required, a rubbing varnish should be speci fied. There is a class of varnishes that dry with a dull gloss, somewhat resembling the effect of rubbed work. These varnishes can be used for the last coat where this dull effect is desired and where the owner is willing to use a substitute in order to save money. They are probably as durable as a rubbed finish, but they lack the smoothness and beauty of a dead finish produced by rubbing. Moreover, a little more gloss is left than is found in the rubbed surface.
Furniture varnishes are usually inferior to first-class architectural varnishes, and should not be specified where good work is desired.
Floor varnishes are specially made to stand hard wear. They are made so as to dry quite quickly—some of them drying over night—and as a rule they will stand considerable hard usage. Floor varnishes are generally made with less body than other finishes, and will consequently spread over a larger surface, leaving a thinner film of varnish. This is one thing that makes them dry more quickly than the ordinary var nish, and thin coats on a floor are less liable to mar from heel marks.
Spirit Varnishes. The two spirit varnishes most generally employed by painters are shellac and gum damar. Shellac is dissolved in alcohol or "cut" with alcohol, as the painters say, to produce shellac varnish; and gum damar is dis solved in turpentine, with the addition of some absolute alcohol, to produce damar finish.
Shellac, when pure, is one of the most val uable materials used by the painter. Not only does it produce a hardwood finish of a beauty difficult to surpass and of great durability when not exposed to the influence of moisture, but it is almost essential as a sap and knot killer under paint. Shellac is often adulterated with rosin. Pure shellac causes no discoloration.
Shellac may be cut with either grain or wood alcohol. The grain alcohol shellac is much su
perior in every way, flowing freer under the brush and not showing laps, something difficult to avoid in using wood alcohol shellac.
Damar varnish is used chiefly in making enamels or in varnishing over enameled wood work. Mastic varnish is used for coating oil paintings. Sandarac varnish is used for polishing.
Amber varnish is sometimes referred to, but is practically never met with in ordinary wood finishing. It is believed that the varnish used by the celebrated Italian violin makers was made by fusing amber. Amber is so difficult to fuse that it is possible to make only a few ounces of amber varnish at a time, this fact precluding its use in modern times when, in order to make any profit, all manufacturing operations must be carried on upon a large scale.
Various Kinds of Stains. While some woods are of such natural color that they present a pleasing appearance when the beauty of their grain is brought out by varnish, wax, or other finish applied upon the bare or filled wood, as a rule most woods need some treatment to alter their color, either by deepening it or by chang ing it altogether in order to bring the woodwork into harmony with the general decorative scheme of the apartment. This process of changing color without hiding the natural grain of the wood is accomplished by staining or dye ing. The methods used in staining wood vary considerably owing to the nature of the wood to be stained or to the special effect desired.
The principal varieties of stains are oil stains, water stains, alcohol or spirit stains, acid and alkali stains, pigment or wiped stains, wood dyes, and the fuming process. The color of open-grained woods, like oak, ash, chestnut, etc., may be modified by coloring the paste filler by adding some pigment to it. In addition to the above methods of staining, all of which are used by the painter and hardwood finisher, there are large quantities of stains sold that are intended principally for the use of the amateur who wants to stain and finish in one operation and who does not possess the mechanical skill or technical knowledge needed to use a true stain. There are two classes of stains of this kind. The first, known as "varnish stains," consist of varnish mixed with some dry pigment ground in it. These varnish stains, as before explained, re quire constant stirring while using, to prevent the pigment from settling out or the color from running streaky. Such stains are suitable only for household work, touching up chairs and the like that have become disfigured and rubbed, or finishing some small article, and are entirely unsuitable for finishing the woodwork of a new house.