Varnish, a clear liquid composition, which by age, and exposure to the air, becomes hard, without losing its transparency : it is employed by painters, carvers, gilders, and other artisans, for imparting lustre to their works, while it defends or preserves them from the effects of dust, moisture, and air.
Varnishes are of various colours, derived from the ingredients of which they consist: their bases are resins, dissolved in fixed oil, in volatile oil, or in alkohol; and, accordingly as either of these fluids are used, the varnishes are distinguished by the names of fat or oily, essential, and spirit-varnish.
Amber-varnish. see vol. i. p. 274.
The fine black varnish, obtained from China and Japan, is a resinous juice exuding from a tree called tsi-chu, and which is conjectured to be the Cashew-nut tree, or Anacardium occidentals; but, being frequently adulterated, it may easily be imitated, by dissolving 4 oz. of gum-lac, a small piece of camphor, and a sufficient quantity of lamp or ivory-black, in 24 oz. of spirit of wine, over a gentle heat, for 24 hours ; the vessel being occasionally shaken. The whole must then be strained, the pure liquid poured into a bottle, and suffered to stand for one or two days, till a clear fluid appear on the surface, which is then fit for use.
Copal, varnish, of a superior quality, may be procured in tire following manner: Take a certain portion of finely-pulverized copal; let it be thoroughly washed in soft or rain-water, then perfectly dried, and put in a glazed earthen vessel well covered, over a moderate coal-fire. After all the gum has been slowly melted, the vessel is to be removed from the fire, and halt the quantity of prepared linseed-oil must be added, by gradually dropping it into the former; both being in a state nearly boiling. In order to prepare the latter, take one pound off pure linseed-oil, and an equal quantity of filtrated water ; pour them together into a new earthen or tinned vessel ; place this mixture over a fire, and suspend the following five ingredients in a coarse linen bag, which, however, must not touch the bottom ; namely : amber, green and white, vitriol, litharge of gold, and red-lead; of each half an ounce. When the oil begins to foam, all.
feculent matter should be skimmed off the surface, and the liquor be suffered to boil very slowly, till the water be completely evaporated ; an effect, which may be readily ascertained, if the height of the oil in the vessel has been previously measured. After the two different ingredients have been incorporated in the manner above directed, and have become cool, they ought to be diluted with oil of turpentine. In the course of two or three days, all the coarse particles will subside; and the clear liquor should then be carefully decanted, or rather filtred, through fine linen. Thus, a white and transparent varnish may be obtained : it is of extensive use for all light grounds, and is remarkably improved by age. If it be required of a harder consistence, it will be advisable to employ equal quantities of white amber and gum-copal, instead of the latter substance alone.
Another excellent white varnish may be made, by infusing 8 oz. of pulverized sandarach, and 2 oz. of Venice turpentine ; with 32 oz. of highly-rectified spirit of wine, in a glass vessel, the orifice of which must be covered with a bladder, and pierced with a pin that is suffered to remain there. The whole is exposed for 8 days to the rays of the sun, or in warm sand, near a fire, and frequently shaken. When all the ingredients are dissolved, it should be allowed to stand at rest, till the liquor become pellucid ; after which it must be decanted into another vessel, and will then be fit for any purpose required.
A yellow varnish may be prepared by dissolving separately, 2 oz. of pure gum-lac, in 48 oz. of alko-hol, and 1 oz. of dragon's-blood in the same quantity of spirit: the solutions must then be mixed, and 3 grains of yellow-wood be added : the whole is then suffered to digest for 12 hours in a gentle heat; when the liquor should be filtred through blotting-paper, and preserved for use, in bottles closely stopped. - This preparation is chiefly employed for imparting a gold colour to brass, or iron; and, when applied to leather that has previously been ornamented with tin-foil, it communicates a similar colour.
All varnishes ought to be secured from the dust: when used, they must be laid on lightly, but quickly, with a clean brush : the substance, thus coated, should then be exposed, if in summer, to the heat of the sun, or in a warm room, being covered with a glass case, to exclude dust; and, when perfectly dry, they ought to be polished with a smooth piece of pumice-stone. - See also Pales; and, in the Appendix, article Iron.