(b) Basic colors. Colors of a basic nature, which form compounds with tannic acid, insoluble in water, and which dye the vegetable fibers with the aid, and animal fibers without the aid, of mordants.
(c) Acid colors. Colors of an acid nature, which dye the animal fibers without the aid of mordants.
(d) Mordant colors. Colors which are dyed with the aid of metallic mor dants. Most of the natural coloring matters come under this head.
(e) Sulfur colors. Colors of recent discovery. Most of them are insoluble in water, but soluble in water contain ing sodium sulfid. They are used for vegetable fibers as direct col- ors, and are similarly applied.
(f) Miscellaneous colors. These include those having little in com mon, and require individual treatment. Some of the most important come under this head.
(1) Indigo. See same in list of natural coloring matters.
(2) Eosines and rhodamines. Especially valuable for pro ducing brilliant pigments in conjunction with metallic pre cipitants, for making artifi cial vermilion, etc.
(3) Aniline black is pro duced by impregnating the cotton yarn or cloth with ani line and the proper amounts of the required chemicals ; on after - treatment, oxidation takes place and the color is formed. Other colors of much importance are produced by processes which con sist essentially in manufacturing the dye in an insoluble form in the goods.
Calico-prinling.
Calico-printing may be considered as local dye ing. It is the art of producing on woven material a design in color by certain processes, one of which is a printing process. The art has been developed from the early painting of cloth in India (in Cali cut, hence the name "calico ") to the modern print. There is probably no other industry in which so great a combination of artistic, mechanical, chem ical and technical skill of the highest order is required, and this, too, to produce so cheap a finished product. Formerly the prints were made from wooden blocks cut in relief, there being a set of blocks equal in number to the colors desired if the pattern were small, or, if large, as many for each color as were necessary to make the complete design. This process is known as block printing and is done by band. For large designs, or for those of more than twenty colors, this method is employed today and to a considerable extent to meet the demand for more artistic goods. The
Japanese produce some very beautiful goods by ap plying the colors with stencils. This method can be used by any one, and very artistic effects can be produced at a trifling expense. In fact, this work should prove most interesting to amateurs, as most elaborate designs may be made.
The modern calico-printing machine consists of a large iron cylinder about which copper rollers are mounted. The cylinder is padded and the design is engraved in the copper rollers, each roller being engraved to apply one color ; as many rollers are necessary as there are colors in the pattern. Beneath each roller is a trough or "color-box " from which the color is carried to the roller by a wooden roller covered with cloth, or by a cylindri cal brush. The entire surface of the copper be comes coated with the color, but as it revolves, a sharp blade, known as the "doctor," scrapes off all the color except that in the engraved part. The cloth to be printed passes between the large cylin der and the copper rollers, and the color is trans ferred to it. With one passage the entire design is produced. In order to give it a resilient surface, an endless web, called the blanket, also passes through, and between it and the cloth to be printed un bleached cloth passes, which serves to take up the surplus color. A second "doctor," called the lint doctor, removes any loose fibers from the copper roller. The rollers are so mounted in the framework that they may be adjusted while the machine is in operation, so that any misfit can be corrected. As the cloth passes from the machine it is dried and given such other treatment as the style of work may require.
Pigments are printed by being mixed with blood albumen, or the white of egg, for delicate shades. On steaming the printed goods, the albumen is coagulated, becomes insoluble and fixes the color. Basic colors are mixed with tannin and acetic acid, in which the tannin lake of the color is soluble ; in drying, the acetic acid evaporates and the insoluble lake is produced. Mordant colors are similarly applied.