Lac, or Gum-Lac is a kind of wax, of which a species of insects form cells upon trees, like honeycombs. See the article Coccos, spec. 5. In these cells remain some of the dead insects, which give a red colour to the whole substance of the lac. That called stick-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 sticks, and grossly powdered, and deprived of its colour by digestion with menstruums, for the sake of the dyes and other purposes, is called seed-lac; when the stick-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 liquified, strained, and formed into thin transparent laminae in the following manner. Separate the cells from the branches, break them into small pieces, throw them into a tub of water count of the for one day, wash off the red water and dry the cells, (Gum Lacca), and with them fill a cylindrical tube of cotton cloth two feet long, and one or two inches in diameter; tie both ends, turn the bag above a charcoal fire; as the lac liquefies twist the bag, and when a sufficient quantity has transuded the pores of the cloth, lay it upon a smooth junk of the plantain-tree (Musa Paradisiaca, Linnaei), and with a strip of the plantain leaf draw it into a thin lamella; take it off while flexible, for in a minute it will be hard and brittle. The value of shell-lac is according to its transparency.
The lac insect is one of the most useful of that tribe yet discovered, particularly to the natives of the countries where it is found. They consume a great quantity of shell-lac in making ornamental rings, painted and gilded in various tints, to decorate the arms of Lacca, the ladies; and it is formed into beads, spiral and linked chains for necklaces, and other female ornaments.—The following are recipes for various purposes to which this substance is applied by them.
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 liquified shell-lac upon the end of your stick (in which manner lump-lac is formed from seed-lac). Knead this upon a wetted board with three ounces of levigated cinnabar; 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 seed-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 liquified lac, beat the stone moderately, and by turning the axis it may 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 Ragaula. It is composed of small angular crystalline particles tinged red with iron, two parts to one of black magnetic land. 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.
5. 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 (fofil alkali); boil an hour more, and add three ounces of powdered load (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 an 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 caseous part of the milk, and remains in the bag, while a limpid acid water drains from it. The coagulum is dried in the shade, and is used as a red colour in painting and colouring.
6. For Dyeing. Take one gallon of the red liquid prepared as before without milk, to which add three ounces of alum. Boil three or four ounces of tamarinds in a gallon of water, and strain the liquor. Mix equal parts of the red liquid and tamarind water over a brisk fire. In this mixture dip and wring the silk alternately until it has received a proper quantity of the dye. To increase the colour, increase the proportion of the red liquid, and let the silk boil a few minutes in the mixture. To make the silk hold the colour, they boil a handful of the bark called load in water, strain the decoction, and add cold water to it; dip the dried silk into this liquor several times, and then dry it. Cotton cloths are dyed in this manner, but the dye is not so lasting as in silk.
The lac colour is preferred by the natives upon flasks of cotton dipped repeatedly into a strong solution of the lac infect in water, and then dried.
Among us lac is also used in various arts; being employed in the preparation of spirit-varnishes, for the making of sealing-wax, and as a colouring material for dying scarlet; see Varnish, Wax, &c. It is insoluble in water; and difficultly soluble in spirit of wine, which for that purpose must be well dephlegmated. According to Neumann, 16 ounces of seed-lac, distilled in an open fire, yielded nine ounces and six drams of a butter or thick oil, one ounce six drams of a watery liquor neither acid nor alkaline, and a residuum weighing two ounces and a half. The colour given by lac is less beautiful, but more durable, than that given by cochineal. To render the colouring matter of the lac diffusible in water, so as to be applied to the stuffs to be dyed, Mr Hellot directs the following process: Let some powdered gum-lac be digested during two hours in a decoction of comfrey root, by which a fine crimson colour is given to the water, and the gum is rendered pale or straw-coloured. To this tincture, poured off clear, let a solution of alum be added; and when the colouring matter has subsided, let it be separated from the clear liquor and dried. It will weigh about 1/4th of the quantity of lac employed. This dried fecula is to be dissolved or distilled in warm water, and some solution of tin is to be added to it, by which it acquires a vivid scarlet colour. This liquor is to be added to a solution of tartar in boiling water; and thus the dye is prepared.
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 a 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 this stick 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.
Lac is likewise employed for medicinal purposes. The stick-lac is the sort used. It is of great esteem in Germany, and other countries, for laxity and sponginess 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 fluor albus, and in rheumatic and scorbutic disorders: it has a grateful smell, and not unpleasant, bitterish, astringent taste.
The gum-lac has been lately used as an electric, instead of glass, for electrical machines. See Lacquer, Lake, and Varnish.
Artificial Laccas, or Lacques, 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 stove fire in a lixivium of pot-ashes 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.