The Dyer's Guide. Chapter IV. On Scouring and Dyeing Wool. On the putrefaction of the woad vat

The Dyer's Guide
Being a Compendium of the Art of Dyeing
Linen, Cotton, Silk, Wool, Muslin, Dresses, Furniture, &c. &c.

With The Method of
Scouring Wool, Bleaching Cotton, &c.
Directions for Ungumming Silk, And For Whitening And Sulphuring Silk And Wool.
And Also
An Inttroductory Epitome of The Leading Facts in Chemistry, As Connected With The Art of Dyeing.

By Thomas Packer,
Dyer and Practical Chemist.

"Cet arte est un des plus utiles et des plus merveilleux qu'on connoisse."
- Chaptal.

"There is no art which depends so much on chemistry as dyeing."
- Garnett.

Second Edition,
Corrected and Materially Improved.

Printed for Sherwood, Gilbert, And Piper,

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.

No one, therefore, should attempt to have a woad vat or vats, unless he can keep them nearly always at work. When worked down in a moderate time, and replenished with lime, woad, indigo, &c., working out and replenishing in, there can be no danger. On the other hand, in proportion as the vat is out of condition, although partially recovered, it must always be with more or less loss.

Ei kommentteja :