Lac, a resinous exudation from the twigs and branches of various kinds of trees in the East Indies, caused by the punctures of the insect coccus ficus, which swarms upon trees yielding a milky juice. The exuding juice forms an incrustation around the twigs, and in this the insects make the cells for containing their eggs. Upon the outside the concrete resinous lumps are marked with numerous pores as if perforated with a needle; within are seen many oblong cells, which often contain dead insects. The substance is of a deep reddish brown, of shining fracture, astringent, and bitterish. It colors the saliva red, and pro-daces a dye of this color but little inferior to the real cochineal. Indeed, before the discovery of the latter it was the material of the fine rich crimson dye of the ancients, and of the durable reds of the dyers of Brussels and Holland. The coloring matter is readily extracted by warm water; the lac itself is for the most part soluble in alcohol, also in an aqueous solution of borax, by which it may be distinguished from most common resins with which it is sometimes adulterated; when burned it diffuses a strong agreeable odor. The crude article broken off with the twigs is known as stick lac, and is sold by those who gather it at from 2 to 4 lbs. for a penny.

When the stick lac is broken up and its coloring matter is partially removed by water, it is called from its granular appearance seed lac. This is sometimes melted into masses and called lump lac. The more familiar variety known as shell lac is prepared by melting the seed lac and straining it through fine linen bags, upon a fiat, smooth surface of wood, to harden. It dries in thin sheets, which break up into small fragments. Their color is from orange to dark reddish brown; they are more or less transparent, hard, brittle, and shining. The substance is soluble in alcohol, but not in water, and possesses neither taste nor smell. It softens readily by heat, so that it has run together in masses when stowed in the hold of a ship. It contains, as found by Hatchett, 90.9 per cent. of resin and 0.5 of coloring matter; the remainder is wax, gluten, and foreign matter. Stick lac contains about 10 Per cent. of coloring matter and 68 Per cent. of resin. The coloring matter is separated by treatment with warm water and evaporation, and, made into square cakes, is known as lac dye, lac lake, or cake lake. When scraped they yield a bright red powder like carmine. A varnish and pigment combined is prepared from stick lac for the process of japanning.

The natives of India employ the substance in various ways. They color it with yellow orpiment and make it into bracelets, chains, and other ornaments in imitation of gold. They prepare with it a good varnish, which they color with cinnabar or some other pigment. The wheels of their lapidaries are covered with a preparation of lac, which by its adhesive nature retains the polishing powders. The chief uses of shell lac are for manufacturing scaling wax, and as the basis for spirit varnishes and the French polish. The best red sealing wax contains 48 parts in 100 of it, together with 19 parts of Venice turpentine, 1 of balsam of Peru, and 82 of finely powdered cinnabar. It forms 60 per cent. of the best black sealing wax, the other ingredients being 10 parts of turpentine and 30 of levigated bone black. The coloring matter and some insoluble ingredients, which are never wholly removed from shell lac, injure it for a varnish for light-colored works; but recent methods of bleaching, one of which by chlorine was introduced by Dr. Hare, have in a great measure removed this difficulty. (See Varnish.) The adhesive quality of lac adapts it for cements for broken porcelain, and united with caoutchouc it makes the famous marine glue.

A weak solution of it in alcohol is recommended in surgery to be spread on bandages for dressing wounds and ulcers. Formerly it was used in medicine, but it has no specific action. - The best stick lac is brought from Siam, and next to this ranks that from Assam. In the best articles the sticks are frequently incrusted entirely around with the lac to the thickness of a quarter of an inch; and the substance also forms large oblong bunches of much greater thickness. The Bengal stick lac is commonly in very scanty and irregular incrustations. The capacity of production is said to be many times greater than the demand, though the annual exportations amount to several million pounds of lac dye and shell lac.