Mordant. (Knight's American Mechanical Dictionary, 1876)

A substance applied to a fabric to give a fixity to the dye. 1. (Dyeing.) Mordants were known to the natives of India, and perhaps of Egypt, in the time of Pliny, who was suffocated by sulphurous fumes  pr carbonic acid in the year 79. "Their fabrics are first imbued, not with dyes, but with dye-absorbing drugs, by which, though they seem to be unaltered, yet when immersed in a caldron of the boiling dye-liquor they are found to be painted. Yet, as there is only one color in the caldron, it is marvelous to see manycolors imparted to the robe, in consequence of the influence of the pigment. Nor can the colors he washed out." He farther remarks to the effect that a number of colors in the caldron would only give a neutral, blended, or confused effect; but, owing to the previous treatment, which made no visible stain, capacity was conferred upon the cloth for so appropriating the color, that different parts obtained different tinctures, according to a specific faculty for adoption and conversion due to the previous preparation in each case.