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So much as this, that only such unstable salts as I have just described, which decompose and yield precipitates by the action on them of alkalis, heat, the textile fibres themselves, or other agencies, are suitable to act as true mordants. Hence, generally, the sources or root substances of the best and most efficient mordants are the metals of high specific appetite or valency.
You will have gums and resins from the wood, calcium chloride from the bleach vats, acids from the "sours"; resin, and resin-soaps; there may also be alumina salts present. Now alumina, lime, resin, and resin-soaps, etc., precipitate dyestuffs, and also soap; if the water is alkaline, some of the mordants used may be precipitated and wasted, and very considerable damage done.
Concerning the Phoenician process of dyeing, the accounts which have come down to us are at once confused and incomplete. Nothing is said with respect to their employment of mordants, either acid or alkali, and yet it is almost certain that they must have used one or the other, or both, to fix the colours, and render them permanent.
The gamins of Tyre employ to this day mordants of each sort; and an alkali derived from seaweed is mentioned by Pliny as made use of for fixing some dyes, though he does not distinctly tell us that it was known to the Phoenicians or employed in fixing the purple.
Chrome Mordanting of Wool and Fur. In studying this subject I would recommend a careful perusal of the chapter on "Mordants" in J.J. Hummel's book, entitled The Dyeing of Textile Fabrics, and pages 337 to 340 of Bowman's work on The Wool-Fibre.
Nature means nothing to be lost, and waste arises from ignorance. She is a royal mistress when royally represented. To the mineral kingdom we are indebted for most of the mordants which fix the hues derived from other sources. That in union is strength is taught by the most common art. Much is yet to be learned in regard to color.
Morder in French, derived from the Latin mordere, means "to bite," and formerly the users of mordants in dyeing and printing believed their action to be merely a mechanical action, that is, that they exerted a biting or corroding influence, serving to open the pores of the fabrics, and thus to give more ready ingress to the colour or dye.
But this is not all, for colours are precipitated as lakes, and mordants also are precipitated, and thus wasted, in much the same sense as the soaps are.
The following mode is, however, a very convenient one for makig experiments on fixing the colouring principles of any vegetable extract: To have several pieces of cloth, woollen, cotton, silk, and linen, dipped in the different mordants, and by keeping a small vessel filled with the colouring solution on a fire in a state a little below boiling, by cutting small pieces of each, and immersing them in the colour, and examining and comparing with each other.
II. Adjective colours, fixing themselves only in conjunction with a mordant or mordants on animal or vegetable fibres, and including all the polygenetic colours. III. Mineral or pigment colours.
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