In the preparation of spirit and turpentine varnishes, scarcely any apparatus is required; as, generally speaking, the process is almost limited to mixing the resins and solvent together, and agitating the whole until the resin is thoroughly dissolved. Heal is not generally necessary, and although frequently resorted to in order to facilitate the dissolution of the resins, in most instances only a moderate degree of warmth is required; consequently the preparation of spirit and turpentine varnishes is far more manageable than that of oil varnishes, and entails much less risk of accident.

The resins should be thoroughly free from moisture, and are generally broken into small pieces, in order that they may be dissolved more quickly, and all impurities are carefully picked out; after which the finest and clearest pieces are generally selected and set aside for making small quantities of varnish of a superior quality. Sometimes, with the view of expediting the dissolution of the resins, they are finely powdered before they are added to the solvent; but, in this case, it is necessary that the agitation should be maintained from the time the resin is added until it is thoroughly dissolved, otherwise it is liable to agglutinate into one mass, that is afterwards very difficult of solution.

In making turpentine varnishes without heat, in quantities of ten or twelve gallons, the resin and turpentine are generally introduced into a large can with a wide mouth, and agitated by stirring with a stout stick; a number of wooden pegs or nails are mostly driven into the stick, near the lower end,to increase its effect.

Spirit varnishes are generally made in smaller quantities; and, to prevent the evaporation of the spirit, the mouth of the vessel is mostly closed and the vessel itself is agitated. In making quantities of four to eight gallons, the resin and solvent are sometimes introduced into a small cask capable of containing about double the quantity, and mounted to revolve on central bearings at the ends. The cask is made to revolve either with continuous motion by a winch-handle, or with an alternating motion by means of a cord passed around the barrel and terminating in a croos-handle, which the operator pulls to give motion to the barrel in the one direction, and the momentum of which suffices to coil up the cord ready for the following pull, which causes the barrel to revolve in the opposite direction, and so on continually.

Quantities of varnish not exceeding two or three gallons, are generally agitated in a tin can, rolled backwards and forwards upon a bench covered with an old carpet or a sack; but whatever method is adopted for the agitation, it should be continued, without intermission, until the resin is sufficiently dissolved to prevent the risk of its becoming agglutinated; the time required for which depends upon the solubility of the resin and the strength of the spirit, but is commonly from three to four hours. The farther agitation for the thorough solution of the resin maybe either continuous or intermittent, according to convenience, but it should not be abandoned until the solution is perfect; and when it is judged to be complete, the varnish is poured into another vessel for examination; and if any of the resin is not perfectly dissolved, the whole is returned to the vessel for farther agitation. When the resin is all dissolved, the varnish is allowed to stand for a tew hours, that any impurities may settle to the bottom, and the clear varnish is lastly strained through muslin or lawn into bottles, and allowed to stand for a few days before use.

Very small quantities of varnish are generally made in glass bottles, large enough to contain about one-third more than the quantity introduced, and they are shaken up at frequent intervals; but although, from the small bulk of the resin, it cannot agglutinate into so insoluble a mass as when larger quantities are made, still, when the agitation is intermitted, several days are frequently required before the resins are entirely dissolved, as the solution depends more upon the amount of agitation than the length of time the resins are submitted to the action of the solvent.

Sometimes, with the view of preventing the agglutination and facilitating the dissolution of the resins, coarsely-pounded glass is introduced with the resin and solvent; in this case the glass should be thoroughly washed and dried, and afterwards sifted, to exclude all the smaller particles, which, from their lightness, would have little effect in. preventing the aggregation of the resin, and would be more troublesome to separate from the varnish.

When heat is employed in making spirit varnishes, the lowest temperature should be used that will suffice to dissolve the resins, as otherwise there is risk of losing a considerable portion of the alcohol by evaporation, thereby reducing the strength of the spirit; the varnish is also liable to be made of a darker color by excess of heat, and those containing shell-lac are less clear and hard when made with heat than when made quite cold, as the heated spirit dissolves the greater portion of the wax contained in the shell-lac, and which becomes disseminated throughout the mass; but when the solution is made without heat, the principal portion of the wax and other impurities remains undissolved at the bottom.

In making large quantities of spirit varnish with heat, a still and worm are sometimes employed, in order to prevent loss by evaporation; the still is heated by a steam or water-bath, and the resins and solvent are agitated by a stirring-rod passing through a stuffing-box in the head of the still. Quantities of two or three gallons are generally made in a tin can, which is dipped at frequent intervals into hot water, and agitated between every dip by rolling; but in this case it is necessary to loosen the cork every time it is immersed in the hot water, in order to allow the vapor of the spirit to escape; otherwise the cork would be driven out with great force, and some of the spirit might be thrown on the lire with great risk of serious accident. Glass bottles, although convenient from their transparency, should never be employed for making varnish with heat, as they are liable to break from the alternations of temperature. They are, however, often used for making small quantities, and in this case the safer practice is to heat the water only in a moderate degree, and to allow of the continuous escape of the vapor through a small notch cut lengthwise in the cork, and which may be closed by the thumb when the bottle is shaken. There is, however, always some little risk of accident in making spirit varnishes near an open fire, when much heat is employed; and a water or sand bath, placed on the top of a stove, so as to be heated only in a moderate degree, will be generally found to afford sufficient warmth, and is, perhaps, the most safe and convenient arrangement for occasional purposes. Shell-lac never requires more than a very moderate warmth to dissolve it, and the solution is frequently made in stone bottles,. placed near a fire and shaken occasionally. When it is required to be very clear, as for metal lacker, it should be passed through filtering-paper, before it is bottled.