Br Bancroft recommends a method of dyeing scarlet, in which a much smaller portion of cochineal produces an equal effect. lie conceived scarlet, from his experiments, to be a compound colour, caused by about three-fourths of crimson or rose colour, and one-fourth of pure bright yellow. He therefore supposed, that, when the natural crimson of the cochineal is made scarlet, by the usual process, a fburth of the colouring mat ter of the cochineal must be changed from its natural crimson to a yellow co lour by the action of the solution of tin. For this reason he introduced a bright yellow dye into the bath with the cochi neal, and reduced the. quantity of this more expensive ingredient. He also found that a mixture of two pounds of sulphuric acid with about three pounds of muriatic acid, poured on fourteen ounces of granulated tin, with expo sure to heat, produced a solution of tin, that had twice the effect of the common nitro-moriatic solution, at less than a third of the expense, and which raised the colours more, without producing a yellow shade. For the yellow dye, Dr. Bancroft used quercitron bark. His pro cess for dyeing scarlet, by the use of this substance, and the above preparation of tin, is as follows : An hundred pounds of cloth are to be put into a tin vessel, nearly filled with water, in which about eight pounds of the murio-sulphuric solution of tin have been previously mixed. The liquor is made to boil, and the cloth is turned through it by the winch for a quarter of an hour in the usual manner. The cloth is then taken out, and four pounds of cochineal, with two pounds and a half' of quereitron bark in powder, put into the bath and well mixed. The cloth is then returned into the liquor, which is then made to boil, and the operation is continued, as usual, till the colour be duly raised, and the dyeing.liquor exhausted, which will usually happen in about fifteen or twenty minutes; af ter which the cloth may be taken out, and rinsed as usual. In this method, the labour and fuel necessary for the second bath are saved ; the operation is finished in much less time ; all the tartar will be saved, as well as two-thirds of the expense of the solvent for the tin, and at least one-fourth of the cochineal usually em ployed; and the colour produced will not he inferior, in any respect, to that dyed with so much more expense and trouble in the ordinary way ; and, moreover, looks , much better than it by candle light.
A rose colour may be readily and cheaply dyed by the above process, by • only omitting the quercitron bark.
Crimson is produced either by dyeing the wool this colour at once, or by first dyeing it scarlet, and then changing the shade to that required. To dye crimson by a single process, a solution of two ounces and a half of alum, and an ounce and a half of tartar, are employed in the boiling for every pound of the stuff, for each of which also an ounce of cochineal is to be afterwards used in dyeing it. It is customary to employ solution of tin, ,. but in smaller proportion than for dyeing scarlet. To render the crimson deeper, and give it more bloom, archil and pot ash are frequently used, but this bloom is extremely fitgacious.
To produce a crimson from a scarlet, the alkalies, alum, and earthy salts are used, all of which have this effect. Crim
son is the natural colour of the cochineal, and to produce it from a stuff dyed scar let, the stuff is boiled for an hour in a solution of alum, the strength of which is to be regulated by the depth of shade required.
Of dyeing Silk red, The red colour obtained from madden ; does not possess sufficient brightness foi silk ; one of the best processes for its use is the following of M. Guhliche ; for every pound of silk, four ounces of alum and one of solution of tin are to be mixed with water ; when the liquor has become clear it is decanted, and the silk is soaked in it for twelve hours, after which it is immersed in a bath of half a pound of madder to each pound of silk, softened by boiling with an infusion of galls in white wine. The bath is to be kept mo derately hot for an hour, and then made to boil for two minutes. The silk is then to be taken out, washed in a stream of water, and dried in the sun. The colour thus obtained is very permanent. By leaving out the galls it is clearer.
Crimson produced on silk by cochineal is called grain crimson, to distinguish it from a colour called false crimson, dyed with Brazil wood. For the grain crimson, the silk, being well cleansed from soap at the river, is to be immersed for a night in alum liquor of the full strength; it is then to be washed, and twice beetled at the river. The bath is prepared by fill ing a long boiler two-thirds with water, to which are added, when it boils, from half an ounce to two ounces of powdered white galls for every pound of silk. When it has boiled for a few moments, from two to three ounces of cochineal, powdered and sifted, are put in for every pound of silk, and afterwards one , ounce of tartar for every pound of cochineal. When the tartar is dissolved, one ounce of solution of tin is added for every ounce of tartar. Macquer recommends this solution of tin to be made by dissolving six ounces of fine grain tin, with two ounces of sal ammoniac, in a pound of ni ' uric acid, diluted with twelve ounces of water. When these ingredients are mix ed together, the boiler is to be filled with _cold water, the proportion of which, for .every pound of silk, is about eight or ten quarts. In this bath the silk is to he immediately immersed, and turned on the winch till it appears of an uniform colour ; the fire is then increased, and the bath is kept boiling for two hours, taking care to turn the silk occasionally ; the fire is afterwards put out, and the silk immersed in the bath, where it is suffered to remain a few hours longer ; it is then taken out, washed at the river, twice beetled, and dried.
To obtain other shades of red, the above processes must be varied. If; af ter the silk has been wrung out of the solution of tin, it is steeped for a night in .a cold solution of alum, in the propor tion of one ounce to a quart of water, wrung, dried, then washed, and boiled with cochineal, it will appear of a pale poppy colour. But a fine poppy-red may be procured by steeping it twelve 'hours in the solution of tin, diluted with eight parts of water, then leaving it all night in the solution of alum, after which it is to be washed, dried, and passed through two baths of cochineal, taking care to add to the second bath a small quantity of sulphuric acid.