Valuable Receipts. To Dye a Dark Blue on Wool.

Scientific American 13, 28.3.1863

We have received several letters recently from persons living in the country, inquiring how to dye a dark bue on wool. To color fast dark blue on wool or woolen cloth, there are only two effective methods practiced by dyers; these consists in using indigo and woad in warm vats. The preparation of these vats and the modes of treating the coloring substances are impracticable to persons who wish to dye small quantities for domestic use. And besides this, it required much experience that cannot be communicated in a receipt to  conduct these processes. We will, therefore, describe more simple modes.

Indigo is the only substance which really can be conveniently used to dye a permanent blue on a limited scale, and at the present prce of this substance the color is expensive by any mode of dyeing. The best Bengal indigo should be selected. It may be known by its deep blue shade  slightly tinged with a copper hue. It must first be reduced to an impalpable powder, then mixed with half urine and soft water in a wooden or stoneware vessel of sufficient size to hold about five pounds of wool for a small batch. The indigo powder is mixed at the rate of eight ounces to ten gallons of urine and placed in a warm situation - about 64° Fah. - and stirred occasionally for five or six days. During the intervals of stirring the vessel should be covered with a thick cloth. The indigo will not dissolve in the liquid or communicate its color to the wool until it is deprived of a certain quantity of oxygen. The urine under fermentation acts pon the indigo chemically, and the liquor gradually becomes deep green in color. This is a sign that the process has proceeded favorably, and the wool to be dyed may now be placed loose in the vessel and stirred occasionally for about an hour then lifted and the liquor squeezed out into the vessel; none of it must be lost. The wool when lifted will be of a deep green color, but upon exposure to the atmosphere it absorbs a certain quantity of oxygen and becomes a dark blue. It may now be washed in cold water, then dried and prepared for carding. A second batch of wool should be treated in the same manner, but its shade will be lighter than the first. It however, may be carded with the first batch and thus produce a medium shade of blue.

To obtain very dark shades of blue two or three vessels made up in the manner described may be used, and the light shades of blue dipped, after being aired, into the stronger blue liquor. This is the only economical way of proceeding when a considerable quantity of wool is to be dyed. The odor of the liquor is very pugent, but the blue thus produced is very permanent and will stand washing and sunshine wihtou fading. Wool will not take on the color unless it is perfectly free from greae; it should, therefore, be washed before it is dyed. This is the old-fashioned method of dyeing blue in the rural districts, and is the most simple, though not a very pleasant operation.

A very dark blue may also be dyed on wool with logwood and the bichromate of potash. The wool being perfectly cleaned, is first boiled in a tin, copper or iron vessel, such as a potash kettle - with one ounce of the bichromate of potash to every five pounds of wool. Sufficient water to allow the wool to be stirred freely with a stick should be used, and the bichromate dissolved in the water before the wool is placed in it. After boiling for half an hour the wool is to be lifted out, aired and allowed to drip until it is in a moist state. The spent liquor of the bichromate of mordant, as it is called, must be thrown away and replaced with clean water. Two pounds and a half of logwood chips placed in a coarse bag are no to be boiled for one hour in the water, then the five pounds of prepared wool are placed therein and boiled for one hour, then lifted out, aired, washed and dried. A very good blue inclining to black is thus dyed, but it is not equal in any respect to indigo.

Copperas may be substituted for the bichromate of potash. Blue vitriol (sulphate of copper is used by many persons in the country to dye blue-blackwith logwood, but this color always fades when exposed to sunlight. A little crude tartar is used by many dyers, mixed with the bichromate of potash and with copperas in the preparation; and with the logwood about one-tenth part of camwood is also used to good advantage. Purslain and carrot tops will color blue on wool, but the processes described are the most convenient. Concentrated logwood which is sold by most druggists may be used instead of chip logwood - a very small quantity of it will suffice to dye a dark color. A deep royal blue may also be dyed with the prussiate of potash and logwood, but the process is intricate. The above mode of dyeing may be practiced by any person with limited conveniences.