VARNISH, a fluid applied to the surfaces of various articles, as wood, kc., and which, by the evaporation or chemical change of a portion, leaves upon them a shining coating, impervious to air and to moisture.
Varnishes may be divided into three classes : alcoholic or spirit var nishes, volatile-oil varnishes, and fixed-oil varnishes.
Spirit or alcoholic varnishes are in general prepared very readily, are easily applied, soon become dry, and emit no disagreeable smell : they are, however, liable to crack or scale off, and are incapable of resisting friction or blows. One kind is made as 'follows :—Mastic 6 ounces, sandarac 3 ounces, reduced to fine powder, and 4 ounces of coarsely powdered glass ; digest in a quart of spirit of wine, contained in a loosely-corked vessel, for three days in a warm room, shaking the mix ture frequently ; then add 3 ounces of melted Venice turpentine to the warm solution, stirring thoroughly till mixed ; let the mixture remain in a warm room for about a week, and then strain it. This is a strong varnish applied to chairs and other articles of furniture. Another consists of copal, which has been liquefied and afterwards very finely powdered, 3 ounces, mastic 2 ounces, and clemi 1 ounce ; digest in a warm room in a quart of spirit, and when the solution is complete add 2 ounces of Venice turpentine. This is stated to form a good varnish for violins and other musical instruments. For different purposes the ingredients of spirit-varnishes are considerably varied ; seed-lac, benzoin, anime, frankincense, entering into the composition, according to the use to be made of them.
The only essential or volatile oil largely used in varnishes is oil, or, as it is commonly called, spirit of turpentine ; and one of the best var nishes into the composition of which it enters is copal varnish. [Corm. Varisism] This is chiefly used for pictures. Another powerful var nish is prepared by adding to highly-rectified oil of turpentine about an eighth of its weight of ersoutehouc ; this, indeed, is the varnish now generally employed in waterproofing the garments well known by the name of Mackintoshes ; sometimes gas-oil, or coal-naphtha, is employed for the same purpose, but its smell is more disagreeable, and longer iu going off. The preparation of this varnish does not require the appli
cation of heat.
In fat or fixed-oil varnishes, the solvent undergoes a chemical change, and dries with the substance dissolved : these are sometimes termed fat varnishes. We shall mention two kinds, first the most colourless : this is prepared by mixing 4 ounces of copal, which has been liquefied and finely powdered, with oil of turpentine and drying linseed-oil, of each 10 ounces ; digest in a gentle heat till the whole is dissolved ; strain it after standing a few days. This forms a solid and nearly colourless glazing, and dries easily at common temperatures. The black varnish used by coachmakere is thus prepared : take of amber 16 ounces, melt it, and add to it half a pint of drying linseed-oil boiling-hot, 3 ounces each of asphalt and rosin, both in fino powder ; stir the materials together till they are thoroughly melted and incorporated, add to the mixture a pint of warm oil of turpentine : this varnish is intended to dry to a very hard consistence.
Dr. Cattell, In 1860, proposed to manufacture varnish by dissolving gums in two kin& of liquids, ethylated and methylated. The gums I are of the usual kind.; but the varnishes are grouped in ono or other of two dudes, according to the elms of solvent employed. Alcohol, wood spirit, methylated spirit, peat oil, shale oil, benzoic, and coal naphtha, are among the solvent, named. Various proportions are named between the ingredients, according to the kind of varnish intended to be produced. We may here mention that Mr. Cooley describe. no leas than misty-four kinds of varnish, of which the chief are placed under the headings of amber, balloon, black, body, bouk binders', carriage, Chinese, copal, crystal, drying, Dutch, etching, flexible, furniture, glass, gun-barrel, hair, india-rubber, Italian, Japan, lao, mahogany, mastio, oak, oil, leather, picture, printers, spirit, toy, transfer, turpentine, and wax varnish.