Schutzenberger gives the following receipts:—

PREPARATION FOR DISCHARGE.
Water2 litres.
Yellow chromate500 grammes.
WHITE DISCHARGE ON BLUE BOTTOM.
Tartaric acid3 kilograms.
Oxalic acid250 grammes.
Burnt starch4 kilograms.
Nitric acid500 grammes.
Water4 litres.

De Kæppelin gives the following:—

WHITE DISCHARGE ON BLUE.
Water2 litres.
Starch1 kilogram, 800 grammes.
Oxalic acid500 grammes.
Tartaric acid250 grammes.
Sulphuric acid375 grammes.

The pieces, having been dyed blue, are then placed in a solution of bichromate of potash in water, which is prepared in the ratio of 50 to 60 grammes to the litre, according to the intensity of the blue. The pieces thus prepared must be dried away from direct solar light or too much heat. In fact, under the action of these agents, the bichromate would be decomposed and the tissue altered. The pieces are often rolled up to prevent this effect. After the pieces are printed, they are passed into a vessel containing water and holding chalk in suspension in sufficient quantity to give it a milky aspect. The temperature of the bath is raised to 60° R. The excess of acid of the color applied is saturated by the chalk, and the excess of bichromate of potash with which the tissue is impregnated is dissolved in the bath. The pieces are afterwards washed and passed through slightly soapy water.

APPLICATION OF INDIGOTINE BY PRINTING.

The first step in the art of printing indigotine upon calicoes was the application of what is called pencil blue. Instead of immersing the fabrics in an indigo vat, the indigo white formed in a very strong indigo vat was thickened and applied locally to certain places on the cloth. The preparation was painted upon the cloth by means of pencils made of willow sticks, the ends of which were broomed up into a kind of brush. The style was hence called pencil blue. The methods now used to apply white indigo locally are of two kinds. The china blue process, and the solid blue process, sometimes called fast or precipitated blue. The china blue process derives its name from the resemblance of its color to the blue on the old china ware. It has great depth of tint, and permanency. It is scarcely used now, except for certain articles requiring great depth of color, such as certain furniture goods, and by the Germans and Swiss for the manufacture of calicoes for exportation to India.

We do not venture to condense the descriptions at our hand of the processes for applying the china blue and the solid blue, and translate those furnished by chemists of high authority. After the method indicated by Darwin in his recent works, we present them in smaller type, with the perhaps unnecessary suggestion that they may be passed over by the general reader.

China blue.—The theory of this printing blue, says Schutzenberger, is very simple. The indigo, reduced to an impalpable powder and thickened, is printed by a plate or roller. After drying, the tissue seems dyed blue, more or less deep, according to the proportion of coloring material used; but it is only a blue of application, which can be removed with the thickening, by the slightest washing. The object is now to reduce and redissolve the indigotine in place to enable it to penetrate the fibre at the end of a consecutive oxidization, and without producing a running of the color or altering the purity and distinctness of the contours of the design. I owe to M. Ed. Schwartz some valuable hints upon the fabrication of this style, which is also described with much care and details in the treatise on printing by M. Persoz.

The reduction of the indigo is obtained by alternate passages of the printed tissue into vats containing,—the first, quicklime slacked; the second, sulphate of iron; the third, soda. The operation is terminated by a passage through a bath of sulphuric acid, which removes the oxide of iron and precipitates the indigo white by hastening its oxidation.