A vat which contains no woad, is called an indigo-vat. For this vat, the indigo is rendered soluble in water by potash instead of lime ; a copper vessel is used, and six pounds of potash, twelve ounces of madder, and six pounds of bran, are boiled with every 120 gallons of water; six pounds of finely-ground indigo are then added, and, after carefully raking it, the vat is covered, and a slow fire kept round it. Twelve hours afterwards, it is to be raked a second time, and this operation is to be repeated at similar intervals of time, till the dye becomes blue, which will generally happen in forty-eight hours. If the bath be properly managed, it will be of a green colour, covered with coppery scales, and a fine blue scum.
The dye called Sawn blue is made with the solution of indigo in sulphuric acid. Take four parts of sulphuric acid, and pour them on one part of in 'digo, in fine powder; let the mixture be stirred for some time, and after it has stood twenty-four hours, add one part of dry potash ; let the whole be again well sti eel, and after it has stood a day and a night, add gradually more or less water. The cloth to be dyed, must be prepared with tartar and alum, and more or less indigo must be put into the bath, according to the shade required. For deep shades, also, the cloth must be passed several times through the bath ; light shades may be dyed after deep ones, but they will not have the lustre given by a fresh bath.
Reds are a very important class of colours, and are furnished by a great number of substances. They all depend, either for their fixedness or beauty, upon the use of mordants; the principal of them are kermes, cochineal, archd, madder, carthamus, and Brazil-wood. Pewter boilers, or well-tinned copper, must be used in preparing all red baths.
The shades of red are usually distinguished into three classes ; namely, the madder red, crimson, and scarlet. Madder is employed for coarse goods. It gives out its colour to water ; and the bath prepared with it is not made hotter than what the hand can bear, until the wool has been in it about an hour, when it may be boiled for a few minutesjust before the wool is taken out. It may be used in the proportion of one-third or one-fourth of the wool dyed. Cloths are prepared for the madder-bath, by boiling them for two or three hours in a solu tion of alum and tartar ; after having been taken out of which, they are left to drain for • few days in a cool place before they are dyed. The use of archil gives a fine but transient bloom to the madder dye. Archil and Brazil-wood, from their perishableness, are seldom used to wool, except in this way, as auxiliaries.
When sulphate of copper is employed as the mordant, madder dyes a clear brown, inclining to yellow. Tin brightens its colour, but not materially.
Hermes has not been much used since the art of brightening cochineal with tin was discovered, as it has not so fine a bloom as the latter dye, though it possesses greater durability. Hermes imparts its colour to water ; and the quan
tity of it used, is, for a full colour, at least three•fourths of the weight of the wool employed. The wool is put in at the first boiling, after having been pre viously prepared by boiling it for half an hour in water with bran, and after wards two hours in another bath, with one-tenth of tartar dissolved in sour water, and then leaving it for a few days in a linen bag.
The red colour of the flowen of carthamus is extracted by s 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 sallower 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 mud 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 solu tion 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 mintaes alter which, the cloth may be taken out and rinsed. In this method, the lake and fuel necessary in the common process for the second bath are saved: tie operation is finished in much less tame; 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 d the cochineal usually required; the colour, at the same time, will not be in any r t inferior to that produced in the ordinary way, at so much more trouble expense, and it will even look better by candle-light than others.