A Dictionary of Arts: Lac, Lac-Dye.

A Dictionary of Arts, Manufactures, and Mines; containing A Clear Exposition of Their Principles and Practice

by Andrew Ure, M. D.;
F. R. S. M. G. S. Lond.: M. Acad. M. S. Philad.; S. PH. DOC. N. GERM. Ranow.; Mulh. Etc. Etc.

Illustrated with nearly fifteen hundred engravings on wood
Eleventh American, From The Last London Edition.
To which is appended, a Supplement of Recent Improvements to The Present Time.

New York: D Appleton & company, 200 Broadway. Philadelphia: George S. Appleton, 148 Chestnut St.


LAC, LAC-DYE (Laque, Fr.; Lack, Lackfarben, Germ.), Stick-lac is produced by the pucture of a peculiar female insect, called coccus lacca or ficus, upon the branches of several plants; as the ficus regiosa, the ficus indica, the rhamnus jujuba, the croton laccuferum, and the butea frondosa, which grow in Siam, Assam, Pegu, Bengal, and Malabar. The twig becomes thereby incrusted with a reddish mammelated resin, having a crystalline-looking fracture.

The female lac insect is of the size of a louse; red, round, flat, with 12 abdominal circles, a bifureated tail, antennæ, and 6 claws, half the length of the body, The male is twice the above size, and has 4 wings; there is one of them to 5000 females. In November or December the young brood makes its escape from the eggs, lying beneath the dead body of the mother; they crawl about a little way, and fasten themselves to the bark of the shrubs. About this period the branches often swarm to such a degree with this vermin, that they seem covered with a red dust; in this case, they are apt to dry up, by being exhausted of their juices. Many of these insects, however, become the prey of others, or are carried off by the feet of birds, to which they attach themselves, and are transplanted to other trees. They soon produce small nipple-like incrustations upon the twigs, their bodies being apparently glued, by means of a transparent liquor, which goes increasing to the end of March, so as to form a cellular texture. At this time, the animal resembles a small oval bag, without life, of the size of cochineal. At the commencement, a beautiful red liquor only is perceived, afterwards eggs make their appearance; and in October or November, when the red liquor gets exhausted, 20 or 30 young ones bore a hole through the back of their mother, and come forth. The empty cells remain upon the branches. These are composed of the milky juice of the plant, which serves as nourishment to the insects, and which is afterwards transformed or elaborated into the red colouring matter that is found mixed with the resin, but in greater quantity in the bodies of the insects, in their eggs, and still more copiously in the red liquor secreted for feeding the young. After the brood escapes, the cell contain much less colouring matter. On this account, the branches should be broken off before this happens, and dried in the sun. In the East Indies this operation is performed twice in the year; the first time in March, the second in October. The twigs incrusted with the radiated cellular substance constitute the stick-lac of commerce. It is of a red colour more or less deep, nearly transparent, and hard, with a brilliant conchoidal fracture. The stick-lac is the best; a piece of it presented to be my Mr. Rennie, of Fenhurch-street, having an incrustation fully one quarter of an inch thick all round the twig. The stick-lac of Assam ranks next; and last, that of Bengal, in which the resinous coat is scanty, thin and irregular. According to the analysis of Dr. John, stick-lac consists, in 120 parts, of -
An odorous common resin - - - 80.00
A resin insoluble in ether - - - 20.00
Colouring matter analogous to that of cochineal - - - 4.50
Bitter balsamic matter - - - 3.00
Dun yellow extract - - - 0.50
Acid of the stick-lac (laccic acid) - - - 0.75
Fatty matter, like wax - - - 3.00
Skins of the insects and colouring matter - - - 2.50
Salts - - - 1.25
Earths - - - 0.75
Loss - - - 4.75

According to Franke, the constituents of stick-lack are, resin 65.7;substance of the lac, 28.3; colouring matter, 0.6.

>Seed-lac. - When the resinous concretion is taken off the twigs, coarsely pounded, and triturated with water in a mortar, the greater part of the colouring matter is dissolved, and the granular portion which remains, being dried in the sun, constitutes seed-lac. It contains of course less colouring matter than the stick-lac, and is much less soluble. John found in 100 parts of it, resin 66.7; wax, 1.7; matter of the lac, 16.7; bitter balsamic matter, 2.5; colouring matter, 3.9; dun yellow extract, 0.4; envelopes of insects, 2.1; laccic acid, 0.0; salts of potash and lime, 1.0; earths, 6.6.; loss, 4.2.

In India the seed-lac is put into oblong bags of cotton cloth, which aare held over a charcoal fire by a man at each end, and, as soon as it begins to melt, the bag is twisted so as to strain the liquefied resin through its substance, and to make it drop upon smooth stems of the banyan tree (musa paradisa). In this way, the resin spreads into thin plates, and constitutes the substance known in commerce by the name of of shell-lac.

The Pegu stick-lac, being very dark-colored, furnishes a shellac of a corresponding deep hue, and therefore of inferior value. The palest and finest shellac is brought from the northern Circar. It contains very little colouring matter. A stick-lac of an intermediate kind comes from the Mysore country, which yields a brilliant lac-dye and a good shel-lac.

Lac-dye is the watery infusion of the ground stick-lac, evaporated to dryness, and formed into cakes about two inches square and half an inch thick. Dr. John found it to consist of colouring matter, 50; resin, 25; and solid matter, composed of alumina, plaster, chalk, and sand, 22.

Dr. Macleod, of Madras, informs me that he prepared a very superior lac-dye from stick-lack, by digesting it in the cold in a slightly alkaline decoction of the dried leaves of the Memecylon tinctorium (perhaps M. capitellatum, from which the natives of Malabar and Ceylon obtain a saffron-yellow dye). This solution being used along with a mordant, consisting of a saturated solution of tin in muriatic acid, was found to dye woollen cloth of a very brilliant scarlet hue.

The cakes of lac-dye imported from India, stamped with peculiar marks to designate their different manufactures, are now employed exclusively in England for dyeing scarlet cloth, and are found to yield an equally brilliant color, and one less easily affected by perspiration than that produced by cochineal. When the lac-dye was first introduced, sulphuric acid was the solvent applied to the pulverized cakes, but as muriatic acid has been found to answer so much better, it has entirely supplanted it. A good solvent (no. 1) for this dye-stuff may be prepared by dissolving 3 pounds of tin in 60 pounds of muriatic acid, of specific gravity 1.19. The proper mordant for the cloth is made by mixing 27 pounds of muriatic acid of sp. grav. 1.17, with 1½ pounds of nitric acid of 1.19; putting this mixture into a salt-glazed stone-bottle, and adding to it, in small bits at a time, grain tin, till 4 pounds be dissolved. This solution (No. 2) may be used within twelve hours after it is made, provided it has become cold and clear. For dyeing, three quarters of a pint of the solvent No. 1 is to be poured upon each pound of the pulverized lac-dye, and allowed to digest upon it for six hours. The cloth before being subjected to the dye bath, must be scoured in the mill with fuller's earth. To dye 100 pounds of pelisse cloth, a tin boiler of 300 gallons capacity should be filled nearly brimful with water, and a fire kindled under it. Whenever the temperature rises to 150° Fahr., a handful of bran and half a pint of the solution of tin (No. 2) are to be introduced. The froth, which rises as it approaches ebullition, must be skimmed off; and when the liquor boils, 10½ pounds of lack-dye, previously mixed with 7 pints of the solvent No. 1, and 3½ pounds of solution of tin No. 2, must be poured in. An instant afterwards, 10½ pounds of tartar, and 4 pounds of ground sumach, both tied up in a linen bag, are to be suspended in the boiling bath for five minutes. The fire being now withdrawn, 20 gallons of cold water, with 10½ pints of solution on tin being poured into the bath, the cloths is to be immersed in it, moved about rapidly during ten minutes; the fire is to be then re-kindled, and the cloth winced more slowly through the bath, which must be made to boil as quickly as possible, and maintained at that pitch for an hour. The cloth is to be next washed in the river; and lastly, with water only, in the fulling mill. The above proportions of the ingredients produce a brilliant scarlet tint, with a slightly purple cast. If a more orange hue be wanted, white Florence argal may be used, instead of tartar, and some more sumach. Lac-dye may be substituted for cochineal in the orange-scarlets; but for the more delicate pink shades, it does not answer so well, as the lustre here is apt to be impaired by the large quantity of acid necessary to dissolve the colouring matter of the lac.

Shelllac, by Mr. Hatchett's analysis, consists of resin, 90.5; colouring matter, 0.5; wax, 4.0; gluten, 2.8; loss, 1.8; in 100 parts.

The resin may be obtained pure by treating shellac with cold alcohol, and filtering the solution in order to separate a yellow gray pulverulent matter. When the alcohol is again distilled off, a brown, translucent, hard, and brittle resin, of specific gravity 1.139 remains. It melts into a viscid mass with heat, and diffuses an aromatic odour. Anhydrous alcohol dissolves it in all proportions. According to John, it consists of two resins, one of which dissolves readily in alcohol, ether, the volatile and fat oils; while the other is little soluble in cold alcohol, and is insoluble in ether and the volatile oils. Unverdorben, however, has detected no less than four different resins, and some other substaces in shell-lac. Shellac dissolves with ease in dilute muriatic and acetic acids; but not in concentrated sulphuric acid. The resin of shellac has a great tendency to combine with salifiable bases; as with caustic potash, which it deprives of its alkaline taste.

This solution, which is of a dark red color, dries into a brilliant, transparent, reddish brown mass; which may be re-dissolved in both water and alcohol. By passing chlorine in excess through the dark-colored alkaline solution, the lac-resin is precipitated in a colourless state. When this precipitate is washed and dried, it forms, with alcohol, an excellent pale-yellow varnish, especially with the addition of a little turpentine and mastic.

With the aid of heat, shell-lac dissolves readily in a solution of borax.
The substances which Unverdorben found in shell-lac are the following:
1. A resin, soluble in alcohol and ether;
2. A resin, soluble in alcohol, insoluble in ether;
3. A resinous body, little soluble in cold alcohol;
4. A crystallizable resin;
5. A resin, soluble in alcohol and ether, but insoluble in petroleum, and uncrystallizable.
6. The unsaponified fat of the coccus insect, as well as oleic and margaric acids.
7. Wax.
8. The laccine of Dr. John.
9. An extractive colouring matter.

Statistical Table of Lac-dye and Lac-lake, per favour of James Wilkinson, Esq. of Leadenhall-street.

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