Of dyeing Wool blue.
Blue may be dyed by woad alone, which would give a permanent but not a deep blue ; but if indigo be mixed with it, a very rich colour will be ob tained.
The following is the method of pre paring a blue vat, recommended by M. Quatremere. Into a vat about seven and a half feet deep, and five and a half broad, are thrown two balls of woad, weighing together, about four hundred pounds, first breaking them ; thirty pounds of weld are boiled in a copper for three hours, in a sufficient quantity of water to fill the vat ; when this decoction is made, twenty pounds of madder, and a basket full of bran, are added, and it is boiled half an hour longer. This bath is cooled with twenty buckets of water ; and after it is settled the weld is taken out, and it is poured into- the vat ; all the • time it is running in, and for a quarter of an hour after, it is to be stirred with the rake. The vat is then covered up very hot, and left to stand for six hours, when it is raked again for half an hour, ant this operation is repeated every three hours.
when blue veins appear on the surface of the vat, eight or nine pounds of quick lime are thrown in. Immediately after the lime, or, along with it, the indigo is put into the vat, being first ground fine in a mill with the least possible quantity of water. When it is diluted to the con sistence of a thick pap, it is drawn 'off at the lower part of the, mill, and thrown. q thus into the vat. The quantity of indigo depends on the shade of colour required. From ten to thirty pounds may be put to the vat now described.
If on striking the vat with the rake a fine blue scum arises, it is fit for use, after being stirred twice with the rake in six hours, to mix the ingredients. Great care should be taken not to expose the vat to the air, except when stirring it. As soon as that operation is over, the vat is covered with a wooden lid, on which are spread thick cloths, to retain the heat as much as possible. Notwithstanding this care, the heat is so much diminished at the end of eight, or ten days, that the liquor must be re-heated, by pouring the greater part of it into a copper over a large fire : when it is hot enough, it is returned into the vat, and covered as be fore.
This vat is liable to two inconveniences; first, it runs sometimes into the putrefac tive fermentation, which is known bv the fetid odour it exhales, and by the reddish colour it assumes. This accident is re
medied by adding more lime.. The vat is then raked, after two hours lime is put in, the raking performed again, and these operations are repeated till the vat is re covered; secondly, if too much lime is added, the necessary fermentation is re. tarded ; this is remedied by putting in more bran or madder, or a basket or two of fresh woad.
When cloth is to be dyed, the vat is raked two hours before the operation, and to prevent it from coming in contact with the sediment, which would cause inequa•• lities in the colour, a kind of lattice of large cords, called a cross, is introduced; when wool is to be dyed, a net with small meshes is placed over this. The wool or cloth being thoroughly wetted with clear water, a little warm, is pressed out, and dipped into the vat, where it is moved about a longer or a shorter time, accord ing as the colour is intended to be more or less deep, taking it out occasionally to expose it to the air ; the action of which is necessary to change the green colour,. given the stuff by the bath, to a blue. Wool and cloth dyed in this manner, ought to be carefully washed, to carry off' the louse colouring matter; and those which are of a deep blue ought to be even fulled with soap, which cleanses them effectually, without injuring the co lour.
A vat which contains no woad is called an indigo vat ; the vessel used for this preparation is of copper, into which is poured, according to Its capacity, water ; in forty pails of which, six pounds of potash, twelve ounces of madder, and six pounds of bran, have been boiled ; six pounds of indigo, ground in water, are then put in, and after raking it carefully, the vat is covered ; a slow fire is to be kept up round it. Twelve hours after it is filled, it is to be raked a second time, which is to be repeated at similar inter vals of time, till it comes to a blue, which will generally happen in forty-eight hours. If the bath be well managed it will be of a fine green, covered with coppery scales and a fine blue scum. In this vat the in digo is rendered soluble in the water by the alkali instead of lime ; the operation of dyeing with it is the same as the pre ceding.