The Art of Dyeing No. 8.
Blue on Wool. Indigo Blue. The Warm Vat.

Scientific American 23, 17.2.1855

Blue on Wool

All cloth should be made of dyed wool, for the color cannot penetrate so thoroughly into the minute cells of the wool when made into cloth as when in the wool state. The best cloths, therefore, are made of dyed wool, still there is a great deal of black cloth dyed is the piece. These pieces can easily be detected, as the makers of the genuine dyed-in-the-wool cloth weave a selvedge of a different color, while the cloth dyed in pieces cannot show this, and the only way that deception is practiced is by sewing on a selvedge of a different color. Persons purchasing black broadcloth would do well to remember this.

The dyeing of wool differs in no respect from woolen cloth, except in the apparatus; the stuffs employed are the same. The wool is dyed in nets, cloth is dyed by handling on a reel, and woolen yarn by turning it over on pins.

Indigo Blue

The common method of dyeing indigo blue on wool for domestic use, is by steeping finely ground indigo in urine, and keeping it at a temperature of about 62°, for four or five days. It then assumes a deep green color, and the wool may be well handled in it for about half an hour, when it will dye a color in depth according to the strength of the liquor. This is a simple and good method of dyeing indigo blue, but the odor is very unpleasant.

The Warm Vat

It requires greater beat to dye wool than cotton or silk, the vat for dyeing wool therefore, has to be so made that it can be heated up. A perforated steam pipe some distance above the bottom of the vat, secured to its sides by brackets, so as to leave free room for raking, is the most convenient method of heating it. By this plan a wooden vat answers as well as an iron one, and the temperature of the liquor can be regulated with the utmost exactness. The indigo must be ground to an impalpable powder, or it will spot the goods, and also be a cause of loss. Take, for a small vat, six quarts of common flour bran and one pound of ground madder, and boil them in a kettle for two hours. In this liquor dissolve three pounds of potash, then take it off, allow it to settle, and pour the clear into the vat, which must now be filled with water at about 120°, to within six inches of the top. This is for a vat that will contain 250 gallons. Now introduce three pounds of finely ground Bengal indigo, and stir all up with a rake. The vat is now covered with a woolen cloth, and the temperature of the dye house should be maintained at about 62°. It is first left to rest for about ten hours, when it should be opened and raked well, and again covered up, and these operations continued every three hours — during the day time — for three days, when it will have assumed a deep green color, and is then fit for working. A net is let down into the vat, to keep any sediment from rising, and then the goods are introduced and cautiously handled until the depth of shade desired is obtained. The shade will not be deep for a vat of 250 gallons with only three pounds of indigo, but by using six pounds, and the same proportions of madder, bran, and potash, a strong vat will be the result. The beat of the vat for dyeing should be about 120° Fah. The mending and working out of an ash indigo vat, requires great care and attention.

The following is the French method of preparing and keeping the indigo vat for wool, usually termed "Homasel's method," and which, perhaps, has no superior:

"For a boiler of from thirty-six to fifty-four gallon buckets of water, employ four pounds of indigo of a fine copper color, two pounds of madder, eight pounds of pearl ash, or of potash, and one-sixth of a bushel of good bran.

Fill the boiler three-fourths full of soft water; put in four pounds of the alkali, a pound and a half of madder, and a quarter of a bushel of bran. Boil these together for at least four hours; this is absolutely necessary. When the liquor has boiled during that time, let it rest for twenty minutes, and strain it clear from the sediment.

While the bath or liquor is boiling, prepare the indigo, which it is absolutely essential should be bruised into a paste fine enough to pass through a fine sieve, which it must be made to do. The sediment that will not pars through must be ground over again. Put in the indigo, and take care that the boiler be not more than two thirds full; nor should the heat be now permitted to exceed 45 degrees of Reaumur's thermometer, or 133 of Fah., to which degree It should be kept up; a few degrees below this will prevent its working well, and a few degrees above will scald it too much.

In twelve or fifteen hours the liquor will be green, when you must put in one pound of alkali; stir it well, and let it rest twelve hours, always keeping up the same degree of heat. Then put in the rest of the alkali, bran, and madder, and let the liquor boil for five minutes, but no more. Let the liquor now rest, until it be cool enough to empty into the vat; empty it therein, and stir it well; let it rest four hours, when it will have a fine green color and a pleasant smell.

When the wool is dyed, the liquor must be cooled to the degree in which the band can be immersed without inconvenience; that is, rather under than above 133 degrees Fah. Should the vat after working become black, the indigo collects and is not diffused; if it becomes greasy, it leaves white spots on the cloth. In the latter case, put about a gallon and a half of bran in two or three bags, and throw them into the vat; when they have absorbed all the grease they will rise to the top of the vat, when they may be taken out and a refreshing of madder and alkali added, according to the quantity of indigo calculated to remain in the vat. Stir the liquor in the vat; let it rest four hours at the heat of 133° Fah. Stir it well again, and let it again rest four hours. If the vat be black, add a little alkali, and bring up the heat to 133° Fah., for twelve or fifteen hours, till it begins to come to, and then add a little madder and bran. The yarn or wool is handled in any of the known methods.

After having colored twenty pounds of wool, the vat may be slightly refreshed and stirred, and left to settle for four hours; but this refreshment need not be put in unless you observe the vat rather spent, and the green color turning blackish; too much refreshing with madder and bran will make the vat turn greasy.

A vat thus set, will dye thirty pounds of wool a royal blue, for each pound of indigo, and also thirty other pounds a lighter blue, and even give a light blue ground to other parcels intended for greens and browns. — This vat ought to be worked out till it is spent and clear, that there may be no need of the trouble and expense of reheating; and the quantity of indigo should be previously calculated to answer the quantity of blues and greens you contemplate to dye in it. This vat is superior in color, when the indigo is good, to the pastel or woad vat; but when cloth is to be dyed in it, instead of wool, the dyers proceed thus:

For a vat of a hundred buckets of water they employ but four pounds of indigo, which is treated as above. In another small boiler, holding ten or a dozen buckets of water, they set another vat, wherein they employ from ten to twelve pounds of indigo in perfect solution, that is, using the proportions of madder and bran necessary with the alkali to dissolve the indigo. By taking a bucket full or two out of this small vat and pouring it into the large one, the latter is conveniently refreshed, and kept up of any desired strength. Before the cloth is dyed, it is exposed on the grass to bleach, and then fulled, and the large vat is kept rather weak than strong. The bleaching and milling contributes much to the brilliancy of color.

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