A solution of a resin, or of a gum-resin, in a liquid, which being applied to the surfaces of different objects, the liquid evaporates and leaves the solid in a brilliant transparent film. The solids used for making varnishes consist of amber, animé, arsacan, benzoin, colophony, copal, damar, elemi, lac, mastic, sandarach, and common resin. The solvents are, alcohol, ether, wood-naphtha or pyroligneous ether, the oils of turpentine, rosemary, nuts, and linseed. Varnishes, or rather lacquers, are sometimes coloured by one of the following substances: aloes, annatto, cochineal, dragon's blood, gamboge, indigo, red saunders, saffron, and turmeric. The varnish-maker calls his resins gums, and he uses them and the solvents either singly—that is, one gum and one solvent—or a mixture of gums and a mixture of solvents. A good varnish should be durable, both as respects hardness and colour; and in this respect amber is remarkable; but amber-varnish is expensive, and is a long time in drying. Animé should be pale and of large size, and be prepared by scraping, to get rid of its rust-like colour, although it is sometimes prepared by pickling in a strong alkali, accompanied by friction with a broom. The large transparent pieces are sold as body-gum, and the worst quality is used for gold-size and japan black. Animé-varnish is not so tough as amber, and although it dries quickly, it is liable to crack, and to deepen in colour by exposure. Animé is much used in oil-varnishes, and also in copal-varnishes, on account of its drying quickly. Copal, according to Lindley, is produced by Hymenia verrucosa of the East Indies; but the resin known in India as copal, and in England as gum-anime, is the produce of Valeria indica, and in its recent and fluid state forms the Piny varnish of India. It is tenacious and solid, but melts at about 97° Fahr. Copal is imported in lumps of a slightly yellow tint; the finest and palest forming body-gum; the second quality carriage-gum; and the third, or worst quality, when picked, is used for gold-size or japan-black. Copal ranks next to amber in durability, and the varnish becomes lighter by exposure; it is not easy to form it into spirit-varnishes, on account of its little solubility in alcohol. It dissolves in ether, but this is too volatile for practical purposes. The oils of rosemary, spruce, and lavender, are sometimes used as its solvents. Amber, animé, and copal, separately or mixed, may be formed into varnish by softening, by means of heat and stirring in hot linseed oil over the fire. Oil of turpentine is used to impart the necessary fluidity. Such are the oil-varnishes used for the best work, which has to bear exposure to the weather or much friction, such as the panels of coaches, japan work, and house-decoration. The usual basis of spirit-varnishes are lac and sandarach. They are used for cabinet and painted indoor-work. Lac is the basis of most lacquers, and also of French polish. It is harder than sandarach, but the latter is hardened by a proportion of shell-lac or mastic, if required to be kept pale, and of Venice turpentine when it has to be polished. Mastic is a favourite spirit-varnish from its working very easily, and, as it can be removed by friction, it is used as a picture-varnish, and for delicate works of a pale colour. Damar, with turpentine, is nearly colourless, and, mixed with mastic, tolerably hard and flexible, so that it is fitted for maps and similar work. Common resin improves the brilliancy of other varnishes, but makes them brittle. The resin dissolved in turpentine or linseed oil forms a varnish which is used for common purposes.

The preparation of varnishes requires considerable care, or an unpleasant colour may be produced. The linseed oil used for the harder resins should be of a pale colour, properly clarified, and united with the resin at a low temperature. About a quarter of an ounce of magnesia per gallon is used in clarifying, with the assistance of heat, and then some months of repose. If a drying oil be required, sulphate of zinc or acetate of lead is used. A cheap varnish is formed by heating linseed oil gradually to the boiling point, skimming, and slowly sprinkling in about three ounces each of dry litharge and red lead per gallon of oil, boiling for three hours, or until steam and smoke cease to be formed. A rough test, as to whether the boiling has been sufficient, is to dip the end of the feather into the oil, when, if it be burnt off or curl up briskly, the boiling is deemed sufficient. The oil is left to cool very gradually, during which the greater portion of the driers subside. The oil should be kept in close leaden cisterns. If the oil is required to be pale, the driers are white lead, sugar of lead, or sulphate of zinc.

Turpentine is much used, either for dissolving the resins or for thinning oil-varnishes. The turpentine should be clean and limpid, qualities in which it improves by keeping. Turpentine-varnishes dry quicker than oil-varnishes; they are of a lighter colour, but not so durable. Mastic, damar, and common resin, are commonly used in such varnishes. Spirit-varnishes, such as those known as white and brown hard, consist of sandarac and shell-lac dissolved in spirits of wine. Such varnishes are harder and more brilliant than the turpentine, and dry more quickly. The spirit must not contain much water, or it will not dissolve the resins; and, in applying the varnish, the air must be tolerably dry, or the varnished surface will appear cloudy or milky—chilled, as it is called—arising from a partial precipitation of the resins. The varnish-maker judges of the strength of the spirit by setting fire to a piece of paper dipped into it; if the paper be consumed, the spirit is judged to be strong enough; if not, it contains too much water.

Naptha, or pyroligneous ether, is used for cheap varnishes, but the effect is not so brilliant as when the resins are dissolved in spirit of wine.

Turpentine and spirit varnishes are formed either cold or with the assistance of a gentle heat. A high temperature is required in preparing oil-varnishes, and as the materials used are very inflammable, the factory should be removed from other buildings. A large copper is used for boiling the oil, gold-size, japan, and Brunswick black, &c.; it is called a set-pot, and is set in a furnace with a flue winding round it. The resins are fused in a gum-pot, or copper, 2 feet 9 inches high and 9 inches in diameter, let into the opening of a small furnace, and furnished with a long iron handle. There is also a copper boiling-pot, the bottom of which let into a hole in the iron plate of the furnace, is 7 inches high and 20 inches in diameter, with a cylinder or body rising from it 2 feet 10 inches high. This pot has a strong handle on each side. There are also a number of ladles, stirrers, funnels, oil-jacks, brass or copper sieves, and other articles required by the varnish-maker.

In using the gum-pot the fire should not be allowed to rise higher outside the pot than the depth of melted resin within, or it is liable to catch fire. The resin must be constantly stirred and divided with the copper-stirrer during the fusing, and should it swell up, the pot must be removed from the fire for a short time; but when at length the resin has become as fluid as oil, the clarified oil is poured in very Varnish slowly with continual stirring. A clear varnish should be formed in eight or ten minutes, as will be seen by dropping a little of it on a piece of glass. The boiling must be continued until a drop of the varnish, placed between the finger and thumb, can be drawn out into fine threads on separating them. This string-test, as it is called, is to be tried every minute or oftener, and when the boiling is complete, all greasiness in the varnish will have been destroyed.

The varnish is then removed from the fire, and when cold enough for mixing, oil of turpentine is poured in with continual stirring, care being taken not to allow the turpentine to form into vapour, or the varnish will overflow. The varnish is lastly strained, care being taken not to disturb the bottoms.

When varnishes are made on a large scale, the boiling-pot and the gum-pot may be in use at the same time. About 8 gallons of oil are gradually heated in the boiling-pot, and 8 lb. of gum in the gum-pot. When the latter, by diligent stirring, has fused into a clear liquid, and the oil is approaching the boiling-point, the maker and his assistant lift the boiling-pot out upon an ash-bed, formed by sifting dry ashes at the side of the furnace; the maker then returns to the gum-pot, and an assistant ladles a quantity of oil into a pouring-jack, which he puts on the iron plate at the back of the gum-pot to keep it hot. When the gum is nearly fused, the maker calls out, "Ready, oil," and the assistant lifts up the jack to the edge of the pot; and when the maker calls out "Oil," he pours it in, and the boiling is continued until the mixture is clear. The gum-pot is then removed to a stand, and the assistant puts three more ladlefuls into the pouring-jack, and three more into a spare tin. The contents of the gum-pot are then poured into the boiling-pot, which still contains about 3½ gallons of oil. In this operation the boiling-pots sometimes catches fire; but the assistant is ready with a thick piece of wet carpet to throw over the blazing pot, so as to smother the flame. If the gum-pot take fire, it is kept inverted, when the flame will go out of itself. The gum-pot is washed out with half a gallon of turpentine, and a broom called a swish. It is emptied into a tin jack, wiped dry, and another 8 lb. of gum put into it and fused. This and another run are treated like the first, when the boiling-pot has a charge of 8 gallons of oil and 24 lb. of gum. It is heated until a froth or scum covers the surface, when the pot is lifted out upon the ash-bed, and the froth stirred down. In this way the boiling may be continued three or four hours, but the time varies with the state of the weather, the quality of the oil, of the gum, the driers, and the state of the fire. When it is decided by the string-test that the boiling is satisfactory, the pot is removed to the ash-bed, and the varnish stirred down until cold enough for the mixing. From 12 to 15 gallons of turpentine are gradually poured in, after which the varnish is strained and stored away. The boiling-pot, ladles, stirrers, &c., are well cleaned with the turpentine used in washing the gum-pot.

In preparing some of the finer varnishes, such as artists' virgin copal, the powdered resin is mixed with powdered glass, 3 lb. of copal to 2 of glass; the glass, by separating the particles, allows the copal to be fused at a more moderate heat. To this quantity 3 quarts of very hot clarified oil are poured in and boiled until it strings freely between the fingers; it is to be thinned with 5 quarts of old turpentine, strained, and kept in an open jar, exposed to air and light, until of sufficient age for use.

The best copal varnishes are slow in drying, as they are made without driers, which injure their brilliancy, colour, and durability. A quicker-drying varnish is formed with amine instead of copal, or it may be mixed with copal.

Spirit and turpentine varnishes are made by mixing the dry picked resins and the solvent with repeated agitation, by means of a stick, furnished with pegs at its lower end, or the ingredients may be put into a kind of churn, mounted so as to revolve upon bearings at the ends. Coarsely pounded glass may be added to prevent the resin from agglutinating. When the solution is complete, it is strained through muslin or lawn. When heat is employed for spirit varnishes, it should be by means of a water-bath or a sand-bath, and a still and worm may be used to prevent loss by evaporation. In such case the resins and solvent in the still are kept in motion by a stirrer passing through a stuffing-box in the head. If a pale lac-varnish be required, white or bleached lac may be used, for which purpose the solution of shell-lac in spirit may be heated with recently prepared animal charcoal, strained through silk, and filtered through blotting paper. Chloride of lime may also be used for bleaching lac varnish. Black varnish may be made by mixing fine lamp-black with brown hard varnish or lacquer. A black varnish for metal may be made by fusing asphaltum and shell-lac, and adding turpentine. The recipes for making varnishes are innumerable. We do not give them in this place, because they are much better and more safely prepared by the varnish-maker than by the amateur. In applying varnishes, soft clean brushes are used; and for spirit varnishes, camel hair pencils and brushes. The varnish should be applied in thin coats, and time be allowed for drying between the application of every two coats. The time allowed will depend on the state of the atmosphere; but in general from two to three hours will be required between every two coats for spirit-varnishes, six or eight hours for turpentine, and twenty-four hours for oil-varnishes. Cold draughts and moist air must be avoided, especially during spirit-varnishing, or the surface may become chilled, as already noticed. Previous to varnishing, the surface must be smoothed with fine glass-paper, and minute holes stopped with gum or wax. The first coat of varnish is usually more or less absorbed by wood and porous surfaces, and a second or a third coat may be required to fill up the pores uniformly. The work is next smoothed with fine glass-paper, and two or three coats of varnish are applied. Where the surface is very absorbent, size is sometimes put on instead of varnish. Coloured works receive their coat of colour before being varnished. The splendid lustre given to the finest kinds of varnish-works is produced by a large number of layers of varnish, and repeated rubbings with fine glass-paper between every two or three coats, then with fine pumicestone powder and water on woollen rags; it is next polished with yellow tripoli and water; and lastly with tallow rubbed all over with the ends of the fingers, the tallow being gradually got rid of by dusting the surface with clean wheat flour, and the surface completed by slightly rubbing with a clean old silk handkerchief.

A great deal might be written on japanning, French polishing, lacquering, &c., but enough has probably been stated to give the general reader an idea of the subject of varnishes. See JAPANNING, LACQUER, &c. (c.t.)