-2 2 :> 



DYEING. 





Uc. 



SiKi-lae. 



Shell-lac. 



I.ac im- 

 proves the 

 colour of co- 



Solvents of 

 Uc, 



, .,1 

 L>r Ban- 

 croft. 



H of a pure red, perfectly transparent, except in 

 the rent i e, which exhibits evident marks of the embryo 



forming." 



112. The cells arc filled with a glutinous liquid, which 



to the taste, and of a tine i . ! colour, soluble 

 in water. This liquid is secreted by the insect, and is 

 destined as a food to the embryo, from the time of its 

 animation till able to quit its cell in quest of food. The 

 natives of Assam use it as a dye, and cotton dipped in 

 it makes afterwards a very good red ink. The eggs, and 

 daik coloured glutinous liquid with which they are sur- 

 rounded, communicate a very beautiful red colour to 

 water while they are fre-sh ; but after they have been 

 dried and kept for some time, the colour they afi 

 less bright. " It would therefore be well worth while," 

 savs Dr Roxl urgh, " for those who aie situated near 

 places where the lac is plentiful, to try to extract and 

 : ve the colouring principles by such means as would 

 prevent them being injured by keeping. I doubt not," 

 continues ho, " but in time a method may be discovered 

 to render this colouring matter as valuable as cochi- 

 neal." 



1 13. As an article of commerce, lac is known in Eu- 

 rope under the appellations of stick-lac, seed-lac, and 

 s/icll-lac. The first is the lac in its native state, as 

 it is found adhering to the twigs oil which it was origi- 

 nally deposited. The seed-lac is said to be the stick-lac 

 broke into small pieces, and thus appearing in a granula- 

 ted form. This, however, is a mistake ; seed-lac being 

 the yellowish hard resinous powder, which remains after 

 the red colour of stick-lac has been extracted, as far as 

 it can conveniently be done, by water. Shell-lac is pro- 

 duced from seed-lac, by putting the latter into long cy- 

 lindrical bags of cotton cloth; melting it, by holding the 

 bags over a charcoal fire; and when the lac melts, strain- 

 ing it through the cloth, by twisting the bags. The lac 

 thus strained, is allowed to fall upon the smooth junk of 

 a plantane tree, and is there spread into thin plates. In 

 this form it is brought to Europe, and is chiefly employ- 

 ed in the composition of varnishes and sealing-wax. 



114. For the purposes of dyeing, stick-lac of the 

 deepest colour should be chosen. The colour which it 

 affords is less brilliant than the scarlet obtained from 

 cochineal; but it has the advantage of possessing greater 

 durability. Berthollet says, that it may be employed to 

 good purpose by mixing a certain quantity in the cochi- 

 neal, when, if it be not in too large proportion, the 

 scarlet will be rendered more permanent, without losing 

 any thing of its beauty. 



115. Water dissolves lac, and the decoction is of a 

 deep crimson colour. The solubility is increased by al- 

 kaline substances. Pure potash and soda completely 

 dissolve the different kinds of lac. Pure ammonia, and 

 carbonate of ammonia, also act on its colouring matter. 

 To separate the part soluble in water, and calculate its 

 proportion to the wax or resin, Hellot used to extract it 

 by means of water and mucilage of comfrey, to precipi- 

 tate the colouring matter with alum, and to collect and 

 dry this precipitate, the weight of wliich was only one 

 fifth of the lac. This precipitate is a compound of the 

 colouring matter and alumine : Hellot used it for dye- 

 ing. 



116. Dr Bancroft seems to be of opinion, that lac 

 employed with the nitro-muriate of tin and tartar, might 

 be made to dye scarlets, .equal in vivacity and beauty to 

 any which have been produced from cochineal, and by 



3 



the same means, taking care only to employ them in a 

 proportion soiiiewh.it larger. He ascertained, in the course 

 i I Ins experiments on ibis .suh.-tunrc, that \\.ttci, at the 

 ordinary temperature of the atmosphere between the ; 



. i- 1 and extracted almost MS much of the 

 colour of powdered stick-lac, as when assisted by a boil- 

 ing heat. He discovered also, that water of this tempe- 

 rature extracted the colouring matter dec from other 

 aces, which were dissolved by it at (he boiling 

 point. Having carefully evaporated a few quarts of this 

 cold infusion of [h)W dei cd .-tick-lac, made during some 

 warm days in the early part of September, he obtained 

 an extract, which, when dried and rubbed in a mortar, 

 broke readily into fine |X>wder, and was altei wards i 

 to dissolve almost as readily as refined sugar ; and ha- 

 ving tried this powder to dye small pieces of broad cloth, 

 with the usual mordants, he says he had no difficulty in 

 producing therewith scarlet colours equal to the 

 which could be any where found, and with little more 

 than half as much in weight of the powder as would have 

 been required of cochineal to produce similar colours. 

 In consequence of these results, and considering the low 

 price of stick-lac in the East Indies, he was convinced 

 that this colouring matter might be successfully introdu- 

 ced as a substitute for cochineal. He accordingly com- 

 municate ! his opinion on the subject to the Chairman of 

 the Court of Directors of the East India Company, and 

 offered to disclose the result of his experiments, for a 

 moderate but suitable remuneration. The Committee of 

 Directors, before coming to a final determination, pru- 

 dently proposed the dyeing of a piece of long ell, (the 

 woollen cloth of which the Company's expoits arc chiefly 

 composed,) in order that the practicability of the method 

 might be ascertained on a sufficiently large scale; the 

 samples which Dr Bancroft had produced being taken 

 from small bits of cloth. The first experiment succeeded 

 so well, that tlie colour produced was approved of by 

 very competent judges ; but in some subsequent trials, 

 tlie results fell short of expectation, the colour being de- 

 ficient in brightness. When the decoction of the lac began 

 to acquire a little of the consistency of a .-oft extract, 

 sudden and remarkable diminution of the beautiful co- 

 lour of the liquor was observed. The change was ascri- 

 bed to the absorption of oxygen ; Dr Bancroft having 

 noticed a similar effect produced on logwood in the 

 same circumstances. To obviate this inconvenience, he 

 has proposed to obtain tlie extract by evaporation with 

 the heat of tlie sun only ; but it is extremely doubtful 

 whether the absorption of oxygen from the atmosphere 

 would not take place in an equal degree, during so pro- 

 tracted a mode of extracting the colour. He has also 

 proposed to collect the colouring matter of lac by preci- 

 pitating it from its aqueous solution by the oxide of tin, 

 and aftci letting off the superincumbent water, to separate 

 the precipitate from ail tlie remaining moisture, by sus- 

 pending it in close linen bags, and afterwards drying it 

 in the sun, or even in the shade. One pound of muriate 

 of tin, in which the acid of the ordinary strength (I.l'/O) 

 was saturated with tlie metal, appeared capable of pre- 

 cipitating as much of the colouring 1:1 itter of lac, as, in 

 its effects, would be equal to one pound of cochineal. 

 He accordingly attempted to dye a piece of cloth with 

 this precipitate, but owing to deficiency of colouring- 

 matter, and other causes which lie mentions to account 

 for the failure, the experiment was not successful. He 

 still seems to think, however, that in this, or some other 



Ailjrctirc 

 Colouring 



Mature. 



