Dyes and dyeing

by Charles Ernest Pellew

This color was, later, found to be due to the combination with iron of the peculiar vegetable acid called tannic acid or tannin. This is found in small quantities in the juices of twigs and leaves of many varieties of plants, and, until the introduction of the modern dyestuffs, this process offered the chief method of obtaining grey or black shades upon cotton. At present it is rarely, if ever, used for that purpose, but the compound is still the basis of most of the writing inks on the market.

To make this color, the cloth is soaked for some time in a solution of an iron salt—nitrate of iron, formed by boiling a solution of copperas for a minute or two with a few drops of nitric acid, is preferable to the untreated copperas—and then, after being wrung and slightly rinsed, it is plunged into a bath containing tannic acid. This can be made by dissolving a few tablespoonfuls of the dry tannic acid in some water, or by making a hot infusion of the leaves, twigs, or bark of any plant or tree containing it. Tea leaves contain much tannin, and so do unripe English walnuts and butternuts. Acorns, oak leaves with nut galls on them, the green twigs of alders, and hazelnut bushes, have all been used to form this color.

PLATE III. SAME TOWELLING AS IN PLATE II, AFTER IMMERSION IN IRON SPRING. THE ROUND WHITE PATTERNS ARE MADE BY TIEING

The grey color quickly develops and, after rinsing, the material can be dried and pressed, or dipped again to obtain a deeper shade, first into the iron and then into the tannin bath. The color is a pleasant, soft shade of grey or, if dyed deeply, a black. It is fast to washing, and fairly so to light, though it may become rusty on standing; like the iron buff, it is not fast to acids.

Some interesting examples of the dyeing of cotton cloth with iron buff and iron grey are shown in Plate [I]. They came from the mineral springs at Arima, near Kobe in Japan, where the waters are so saturated with iron salts, that comparatively short immersion, and exposure to air, will bring out a deep orange shade. The Japanese, not content with dyeing their goods plain colors, have for many generations utilized these springs in the production of figures and designs on the cloth. Plate [V] is an example of stencil work, where the white patterns are made by covering parts of the cloth with a “resist paste” which protects whatever it is in contact with from the action of the coloring agent.

Plate [II] shows a piece of soft calico on which impressions of leaves have been made by placing fresh juicy leaves between two pieces of cloth, and beating them with wooden mallets.

Plate [III] shows the same piece of cloth as in Plate [II], after immersion in the iron spring, and exposure to air. The tannin from the leaf juice converts some of the iron oxide into iron grey; while the white figures are made by tying the cloth with string or tape (Tied and Dyed work) before dyeing it.

So far as we can tell, these two were the only mineral colors known to the ancients. Several other mineral colors, however, were in common use by the cotton dyers in the days preceding the introduction of modern dyestuffs, but it is hardly worth while to dwell here on many of them. Yellow and orange shades were obtained by impregnating cloth with lead salts, and then developing with a bath of chromate or bichromate of potash, with more or less caustic alkali added for the darker shades.

Prussian blue, too, was used as a substitute for the more expensive indigo. This was formed by using the nitrate of iron for the first bath, and then developing the color with a bath of yellow prussiate (ferrocyanide) of potash. These colors, however, are so far inferior in their application, and in fastness to light and to rubbing, to the colors now at our command, that they have disappeared entirely for textile work, though they are still widely used for pigments.