LAC, or Gum Lac, is a substance, of which a species of insects form cells upon trees, like honeycombs. This is the coccus lacca, Lin. See ENTOMOLOGY INDEX. In these cells remain some of the dead insects, which give a red colour to the whole substance of the lac. That called flick lac is the wax adhering to some of the small branches of the tree, and which is unprepared. This lac, when separated from the adhering flicks, and grossly powdered, and deprived of its colour by digestion with menstruums for the sake of the dyes and other purposes, is called feed lac; when the flick lac is freed from impurities by melting it over a gentle fire, and formed into cakes, it is called lump lac; and, lastly, that called shell lac is the cells liquefied, strained, and formed into thin transparent laminae. See DYING INDEX.
The following are some of the purposes to which this substance is applied.
1. For sealing wax. Take a stick, and heat one end of it upon a charcoal fire; put upon it a few leaves of the shell lac softened above the fire; keep alternately heating and adding more shell lac until you have got a mass of three or four pounds of liquefied shell lac upon the end of your stick (in which manner lump lac is formed from feed lac). Knead this upon a wetted board with three ounces of levigated cinnamon; form it into cylindrical pieces; and to give them a polish, rub them while hot with a cotton cloth.
2. For japanning. Take a lump of shell lac, prepared in the manner of sealing wax, with whatever colour you please, fix it upon the end of a stick, heat the polished wood over a charcoal fire, and rub it over with the half melted lac, and polish by rubbing it even with a piece of folded plantain leaf held in the hand; heating the lacquer, and adding more lac as occasion requires. Their figures are formed by lac charged with various colours in the same manner.
3. For varnish. In ornamenting their images and religious houses, &c., they make use of very thin beat lead, which they cover with various varnishes, made of lac charged with colours. The preparation of them is kept a secret. The leaf of lead is laid upon a smooth iron heated by fire below while they spread the varnish upon it.
4. For grindstones. Take of river sand three parts, of feed lac washed one part; mix them over the fire in a pot, and form the mass into the shape of a grindstone, having a square hole in the centre, fix it on an axis with liquefied lac, heat the stone moderately, and by turning the axis it may be easily be formed into an exact orbicular shape. Polishing grindstones are made only of such sand as will pass easily through fine muslin, in the proportion of two parts sand to one of lac. This sand is found at Ragimaul. It is composed of small angular crystalline particles tinged red with iron, two parts to one of black magnetic sand. The stonecutters, instead of sand, use the powder of a very hard granite called coruna. These grindstones cut very fast. When they want to increase their power, they throw sand upon them, or let them occasionally touch the edge of a vitrified brick. The same composition is formed upon sticks, for cutting stones, shells, &c., by the hand. For painting. Take one gallon of the red liquid from the first washing for shell lac, strain it through a cloth, and let it boil for a short time, then add half an ounce of soap earth (fossil alkali); boil an hour more, and add three ounces of powdered lead (bark of a tree); boil a short time, let it stand all night, and strain next day. Evaporate three quarts of milk without cream to two quarts upon a slow fire, curdle it with four milk, and let it stand for a day or two; then mix it with the red liquid above mentioned; strain them through a cloth; add to the mixture one ounce and a half of alum, and the juice of eight or ten lemons; mix the whole, and throw it into a cloth bag strainer. The blood of the insect forms a coagulum with the caustic part of the milk, and remains in the bag, while a limpid acid water drains from it. The coagulum is dried in a shade, and is used as a red colour in painting and colouring.
The method of obtaining the fine red lac used by painters from this substance, is by the following simple process: Boil the stick lac in water, filter the decoction, and evaporate the clear liquor to dryness over a gentle fire. The occasion of this easy separation is, that the beautiful red colour here separated, adheres only slightly to the outsides of the sticks broke off the trees along with the gum lac, and readily communicates itself to boiling water. Some of the sticking matter also adhering to the gum itself, it is proper to boil the whole together; for the gum does not at all prejudice the colour, nor dissolve in boiling water; so that after this operation the gum is as fit for making sealing wax as before, and for all other uses which do not require its colour.
6. For dyeing. See Dyeing Index.
Lac is likewise employed for medicinal purposes.—The stick lac is the most used. It is of great esteem in Germany, and other countries, for laxity and sponging of the gums proceeding from cold or a scorbutic habit; for this use the lac is boiled in water, with the addition of a little alum, which promotes its solution; or a tincture is made from it with rectified spirit. This tincture is recommended also internally in the florid album, and in rheumatic and scorbutic disorders; it has a grateful smell, and not unpleasing, bitterish, astringent taste.
The gum-lac has been used as an electric, instead of glass, for electrical machines. See Lacquer, Lake, and Varnish.
Artificial Lacca, or Lacque, is also a name given to a coloured substance drawn from several flowers; as the yellow from the flower of the juniper, the red from the poppy, and the blue from the iris or violet. The tinctures of these flowers are extracted by digesting them several times in aqua vitae, or by boiling them over a slow fire in a lixivium of pot ash and alum.
An artificial lacca is also made of Brazil wood, boiled in a lixivium of the branches of the vine, adding a little cochineal, turmeric, calcined alum, and arsenic, incorporated with the bones of the cuttle fish pulverized, and made up into little cakes and dried. If it be to be very red, they add the juice of lemon to it; to make it brown, they add oil of tartar. Dove-coloured or columbine lacca is made with Brazil of Fernambuc, steeped in distilled vinegar for the space of a month, and mixed with alum incorporated in cuttle fish bone. For other processes, see Colour-Making.