The red colour of the flowers of carthamus is extracted by a weak alkaline ley, and precipitated by lemon juice or sulphuric acid, but is chiefly used for silk, and cotton. The precipitate is used in dyeing, and is called safflower or bastard saffron.
A crimson colour, inclining to violet, is the natural colour of cochineal, which yields most of its colouring matter to water, and, by the addition of a little alkali or tartar, the whole of it is extracted. 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, with an ounce of cochineal, is employed for every pound of stuff. A little nitro-muriate of tin must be added for a fine crimson. Archil gives to crimsons that fine dark shade which is called bloom, but this soon disappears, by exposure to the air and light. For pale crimsons, the quantity of cochineal is reduced, and madder substituted.
Dr. Bancroft first suggested that scarlet was a compound of crimson and yellow, and he founded upon this idea, a more economical mode of producing it than had previously been used. He gives the following directions for dyeing scarlet: - One hundred pounds of cloth are to be put into a tin vessel, nearly filled with water, with 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 quercitron bark in powder, put into the bath and well mixed. The cloth is then returned into the liquor, which is 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, after which, the cloth may be taken out and rinsed. In this method, the labour and fuel necessary in the common process 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 required; the colour, at the same time, will not be in any respect inferior to that produced in the ordinary way, at so much more trouble and expense, and it will even look better by candle-light than others.
By omitting the quercitron-bark, the above process will afford a rose-colour. Scarlet may be changed to crimson by boiling the cloth in a solution of alum (ill the shade desired is obtained. Alkalies and earthy salts in general have the same effect as alum.
Yellow is a colour but rarely required in the dyeing of wool, yet, as it frequently forms the base of other colours, it may be proper to notice it. Weld fustic, and quercitron bark, furnish the best yellows: weld is a plant which is both cultivated and grows wild in this country; the stem is slender, and rises to the height of three or four feet; the entire plant is used in dyeing, and is gathered when it is ripe: the shortest and slenderest stems are the most esteemed. Fustic is the wood of a large West Indian tree. Quercitron grows in great abundance in North America, and is there called yellow oak; its bark is the only part used for dyeing.
The colours obtained from weld and quercitron both nearly resemble each other in shade, and also in durability, which is not great; but the bark containing the largest quantity of colouring matter is not only the most convenient to use, but upon the whole the cheapest. Dr. Bancroft has given the best directions for its use. He directs a deep and lively yellow to be thus prepared for wool: - Let the cloth be boiled for an hour or more, with about one-sixth of its weight of alum dissolved in a sufficient quantity of water; then plunge it without rinsing into a bath of warm water, containing in it as much quercitron bark as equals the weight of the alum employed as a mordant. The cloth is to be turned through the boiling liquid until it has acquired the intended colour. Then a quantity of clean powdered chalk, equal to the hundredth part of the weight of the cloth, is to be stirred in, and the operation is completed. The object which the dyer has in view is to give his stuffs a uniform and durable colour, at the same time that he entirely preserves their original texture. He therefore uses colours in solution, in order that their particles may apply themselves to the individual fibres of the stuff, according to their affinity for it.
When. for example, a quantity of wool, freed from all impurity, is dipped into the solution of any colouring matter, if the fibres of the wool have a stronger attraction for the colouring matter than the water or other menstruum which holds that colour in solution, the colouring matter will leave its solvent, and apply itself to the wool, which will by that means be dyed; its fibres will have become covered with colouring matter; and if their attraction for it be so strong that the action of soap, air, and light, or other ordinary means of exposure, shall have no perceptible effect in decomposing the combination, orin other words, of injuring its tinge, the colour is said to be permanent; so that dyeing is in facta chemical process, and the application of both animal and vegetable bodies depends on their chemical affinities.