Varnish, a solution of resinous matter, used for covering the surfaces of bodies to give them a shining appearance, and to protect them against the air and moisture. The principal substances which enter into the composition of varnishes are: as solid constituents, rosin, amber, mastic, sandarach, lac, elemi, dammar, benzoin, copal, asphalt, and caoutchouc; as solvents, oil of turpentine, linseed, poppy, and a few other vegetable oils, wood naphtha, benzine, and some other constituents of petroleum, alcohol, and ether. As coloring materials, gamboge, dragon's blood, aloes, saffron, annatto, and turmeric are used; to which may be added small quantities of cochineal, French yellow, and other colors, to impart increased brilliancy. Varnishes may be divided into four classes: 1, ether varnishes; 2, spirit varnishes; 3, volatile-oil varnishes; and 4, fixed-oil varnishes. Of the first kind the only one much used is that for repairing the glazing of the colored enamels used in jewelry. It is made by gradually adding five parts of pulverized copal to two parts of sulphuric ether, in a flask which is corked and occasionally shaken for 24 hours or longer.

Spirit varnishes made with alcohol are conveniently prepared, and, on account of their rapid drying and leaving no disagreeable smell, are in frequent use in the household for covering various articles of art or vertu made by amateurs. When large quantities of spirit varnish are made, a still, with a capital and worm, is usually employed. A stirring rod passes through a stuffing box in the capital. The still is heated by a steam or water bath. The materials being placed in the still, the heat is raised until the alcohol begins to distil. The heat is then lowered, and the solution continued with stirring in an equable manner with as little evaporation as possible. When the stirring rod by its easy turning gives evidence of complete solution, the varnish is passed through a silk sieve and then through porous paper, or allowed to clarify in stone jars. The alcohol which may have distilled over should be added to the varnish. Spirit varnishes are liable to scale off or crack, and are incapable of resisting friction or blows. To diminish this tendency, small quantities of oil of turpentine are often added to them, or some of the softer and more adhesive resins are employed in their composition.

The alcohol should not be of less strength than 40° to 36° Baume (sp. gr. 0.830 to 0.849), as otherwise the resins dissolve with much more difficulty, and the varnish will neither be so brilliant nor so drying. Three ways of making the solution are employed, viz.: 1, by simply digesting the resins, etc, in the proper quantity of alcohol, either in the shade or exposed to the sun, occasionally shaking the bottle; this takes a long time, and many substances cannot be dissolved in this way, but the product has the least possible amount of color; 2, by heating over a water bath, which is much more rapid, but produces more highly colored varnishes; 3, by heating over an open fire, which still more changes the color of the resins, and consequently of the varnish, but it is so much more rapid that it is employed almost exclusively for manufacturing purposes. - Oil of turpentine is almost the only volatile oil employed in varnishes, and the most important one into which it enters is copal varnish. (See Copal.) The ingredients and modes of preparation are nearly the same as for spirit varnishes.

An important difference between the two kinds is, that spirit varnishes are injured in quality by keeping, while those with oil of turpentine are very much improved by it, from the more intimate union which takes place between the resins and the oil. - Fixed-oil varnishes are almost entirely made with linseed oil, for which poppy oil is sometimes substituted, and they generally contain also a large proportion of oil of turpentine. The resins used are almost exclusively the different kinds of copal, and amber. In consequence of the slow evaporation of the solvent, and the large amount of residue from it, they are, of all varnishes, the slowest in drying, but the most durable. (See Linseed Oil.) For articles of sheet iron, tin, copper, or brass, and for all articles exposed to constant wear and frequent rubbing, they are particularly adapted. (See Japanning.) In consequence of the difficult fusibility of the copal, a very different process from that used for spirit and turpentine varnishes must be employed in their preparation. The resin is first melted over an open fire; and when perfectly liquid, the linseed oil, heated to 300° or 400° F., is incorporated with it, and finally the oil of turpentine.

It is indeed possible to melt copal directly in boiling oil, and the subsequent addition of a proper quantity of oil of turpentine will bring it to a proper consistence; but as in this case the oil is always more or less burnt, the varnish is both more highly colored and less drying, and this method has been generally abandoned. Great care should be taken that the resins used are of equal fusibility, for if the heat is much raised or long continued after complete fusion of a part, there will be much more color than even if the more infusible parts alone were used. - Besides the four classes of varnishes above described, others are employed for special purposes which can scarcely be included under any of them. Dr. Bolley describes a caoutchouc varnish, which appears to possess valuable properties. The caoutchouc is cut into small pieces and digested in sulphuret of carbon, which forms a jelly with it; and by treating this with benzole, a large proportion will be dissolved. The liquid must be strained through a woollen cloth, and the sulphuret of carbon removed by evaporation in a water bath, after which the liquid may be diluted with an additional quantity of benzole.

A gutta percha varnish is made by dissolving one part of gutta percha in 4 or 6 parts of oil of turpentine, and adding 8 or 10 parts of linseed-oil varnish, boiling hot. It is well adapted for varnishing maps and prints, as it does not affect the whiteness of the paper, does not reflect light disagreeably as resinous varnishes do, and is not liable to scale off. Another valuable varnish, called "milk of wax," is prepared by melting a certain quantity of white wax, adding to it while in fusion an equal quantity of alcohol, of specific gravity 0.83, stirring the mixture, and pouring it out upon a porphyry slab, on which it is ground with a muller until it becomes smooth and homogeneous, when water is mixed in by degrees to the amount of four times the weight of the wax, and the emulsion finally strained through canvas. This may be spread with a smooth brush on the surface of a painting, allowed to dry, then fused by passing a hot iron over it, and when cold rubbed with a linen cloth to bring out the lustre. To some such process as this the ancient paintings on the walls of Herculaneum and Pompeii owe their freshness at the present day.

Prof. Bottger proposes the following black varnish for zinc: Dissolve 2 parts of nitrate of copper and 3 parts of chloride of copper in 64 parts of water, and add 8 parts of nitric acid. Puscher's method is as follows: He dissolves equal parts of chlorate of potash and sulphate of copper in 36 times as much warm water, and leaves the solution to cool. The zinc castings are immersed for a few seconds in the solution, or the sheets may be washed with a sponge, which turns them quite black with oxide of copper. They are then washed and dried, and the coating is rubbed with a cloth, which imparts a glittering indigo appearance. Milk of wax varnish may then be applied, which gives the surface a deep black color and gloss. - The following comprise some of the best recipes for varnishes:

No. 1 is copal varnish for fine paintings; 2, cabinet varnish; 3, best body copal varnish, for bodies of coaches, etc, which require polishing; 4, carriage varnish for parts not requiring to be polished; 5, best white hard spirit varnish; 6, white spirit varnish for violins; 7, brown hard spirit varnish; 8, turpentine varnish; 9, crystal varnish; 10, amber varnish; 11, paper varnish; 12, sealing wax varnish; 13 and 14, black varnishes. - Besides all these compound varnishes, the liquid resins which exude from many species of trees, especially in China, Japan, Burmah, and India, are used as varnishes, either crude or with slight preparation. (See Japanning.) The Chinese varnish is said to be produced by the augia Sinensis, and is black when simply dried, but is colored by various pigments. The Japan varnish of Kämpfer and Thunberg is rhus vernix, and that of the Malayan islands stagmaria verniciflua. The juice of holigarna longifolia is used in Malabar for varnishing shields; the Burmese varnish tree is melanorrhcea, and a fine liquid varnish is yielded by vateria Indica and V. lanceoefolia.

A resinous juice is also employed by the Feejeeans as a varnish or glaze for their pottery.