This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Discharging. A method employed in calico and silk printing for the purpose of imprinting a pattern upon a ground of solid color. If, for example, a piece of calico cloth previously dyed a solid color be marked over with blocks covered with a paste containing tartaric acid wherever the latter touches the cloth, its color will be removed or "discharged," thus producing white spots. Numerous modifications of this principle with other discharging agents, and various coloring matters, are of frequent use for producing colored patterns on solid grounds. In the process most practiced the goods are either padded all over or on one side only, with mordant and dried, and afterward the pattern printed on the portions discharged. [See Calico, Bandanna, Mordant].