Sometimes such a condition of the vat is absolutely irremediable; but when not gone too far, sprinkle some lime into the liquor, and stir it. If you can thus remedy the defect, and bring the liquor to smell of lime, and to feel soft, cover the vat, and let it stand. If, at the expiration of an hour and a half, the effervescence begin, you may put in a pattern; in an hour afterwards, it may be taken out, and regulate your process by the degree of green which the pattern has imbibed; but, in general, when vats are thus out of order, they are not so soon recovered.
To work a vat which is in proper order.
The vat being in a proper state, the cross suspended, and thirty ells of cloth ready, or scoured wool in proportion, designed for black, by dyeing it of a blue grey; and having passed and repassed the cloth through the liquor for a full half-hour, it is to be wound round the winch, and thrown off into the barrow, and aired by the listings to change the green to blue. After this, a second piece may be dyed by the same process.
Having made this overture, or first stirring, as it is also called, the vat must be stirred afresh, adding lime; but not so much as to destroy the proper smell and feel. If the vat be in a good state, on the first day, it may be stirred three or four times; but it must not be overworked, particularly on the second day.
Concerning the colours to be obtained to the best possible advantage from a fresh vat on the first day,—the first is for black, the next for royal blue, and the third a brown green. On the second day, violet, purple, and Turkey blues in the last stirring. On the third day, if the liquor be too much diminished, it must be filled up with hot water. At the end of the week light blues may be done, and on Saturday night add rather more lime, to preserve the vat till Monday morning. On Monday morning add more indigo, and stir the paste; keep the vat liquor at a proper distance from the top. Cover it for two hours; then put in a pattern, and in an hour take it out; add lime according to the green shade of the pattern, and in an hour or two, if your vat has not suffered, you may begin working it afresh.
To keep the cloth, &c. from the sediment, there is always let down into the vat, before the work is begun, an iron circle, with cords fastened from the circumference to the centre.
On the putrefaction of the woad vat.
Whatever be the cause, most certain it is, that the woad vat, even when prepared in the most careful and scientific manner, is soon disposed, if not used, to go into the putrid fermentation; of this we may be satisfied, when it smells like rotten eggs, as stated above.
The loss of a woad vat to dyers is extremely serious, both from the quantity of woad, as well as of indigo, which it contains: these articles being always expensive. The woad vat being worked by heat directly applied from an open fire, (the old method of heating it,) was much more liable to be lost than if it remained cold, or was worked continually, as it usually now is in London; added to which, the more equable application of heat by steam, there is not now the danger which there was in cessation, at uncertain times, and in uncertain states of the vat, as to richness or poorness of woad or of indigo.
But a dyer in the country, whose business is barely sufficient to keep a vat going, will find more difficulty in this respect. If, therefore, he does a small batch of work on Monday, but has not half worked down his vat, and has no prospect for two or three days of doing any more work, he may possibly try to keep it with lime for a day or two: he may do so, and in the issue, in some instances, too much lime is the consequence. We consider, however, that when the vat can be worked daily, and replenished as it is worked down, as is the case in London, with care and attention, there is no danger of the loss of a woad vat: in London, such an accident now seldom happens. The author is, notwithstanding, persuaded that all the art of man cannot always keep a vat from the state of having either too much or too little lime, when heated but seldom, under a short course of work: for when a vat is in order, it is like a ripe vegetable; you must gather it, or it passes the time of its perfection; it may even be rotten ripe. We say, therefore, WORK THE VAT: withdraw from it, upon your cloth, its colour, which, as soon as you expose it to the atmosphere, will combine with its oxygen,—the oxygen with the carbon of the indigo and the woad. If you play with it too long, the putrid fermentation will begin, and the vat will be spoiled. The smell of rotten eggs always proclaims the approach of the mischief.