It is often observed that goods printed upon the same day, and with the same mordant, exhibit inequalities in their tints. Sometimes the colour is strong and decided in one part of the piece, while it is dull and meagre in another. The latter has been printed in too dry an atmosphere. In such circumstances a neutral mordant answers best, especially if the goods be dried in a hot flue, through which humid vapours are in constant circulation.
In padding, where the whole surface of the calico is imbued with mordant, the drying apartment or flue, in which a great many pieces are exposed at once, should be so constructed as to afford a ready outlet to the aqueous and acid exhalations. The cloth ought to be introduced into it in a distended state; because the acetic acid may accumulate in the foldings, and dissolve out the earthy or metallic base of the mordant, causing white and gray spots in such parts of the printed goods. Fans may be employed with great advantage, combined with [Hot Flues]. (See this article.)
In the colour laboratory, all the decoctions requisite for the print work should be ready prepared. They are best made by a steam heat, by means of copper boilers of a cylindric form, rounded at the bottom, and encased within a cast-iron cylinder, the steam being supplied to the space between the two vessels, and the dye-stuff and water being introduced into the interior one, which for some delicate purposes may be made of tin, or copper tinned inside. A range of such steam apparatus should be placed either along one of the side walls, or in the middle line of the laboratory. Proper tables, drawers, phials, with chemical reagents, measures, balances, &c., should also be provided. The most useful dye-extracts are the following:—
Decoction of logwood, of Brazil wood, of Persian berries, of quercitron bark, of nut-galls, of old fustic, of archil or cutbear, of cochineal, of cochineal with ammonia, of catechu.
The following mordants should also be kept ready prepared:—
1. Aluminous mordant.
1. Take 50 gallons of boiling water.
1. Take 100 lbs. of alum.
1. Take 10 lbs. of soda crystals.
1. Take 75 lbs. of acetate of lead.
The soda should be added slowly to the solution of the alum in the water, and when the effervescence is finished, the pulverized acetate of lead is put in and well stirred about till it be all dissolved and decomposed. During the cooling, the mixture should be raked up a few times, and then allowed to settle. The supernatant liquor is the mordant; it has a density of 11° or 111⁄2° Baumé. It serves for reds and pinks, and enters into the composition of puce and lilac.
2. Aluminous mordant.
2. Take 50 gallons of water.
2. Take 100 lbs. of alum.
2. Take 10 lbs. of soda crystals.
2. Take 100 lbs. of acetate of lead;—operate as above directed.
The supernatant liquor here has a density of 12° Baumé; it is employed for lapis resists or reserves, and the cylinder printing of madder reds.
3. Aluminous mordant.
3. Take 50 gallons of water.
3. Take 100 lbs. of alum.
3. Take 6 lbs. of soda crystals.
3. Take 50 lbs. of acetate of lead;—operate as above directed.