Page:Arts & Crafts Essays.djvu/229

 ambers, maize-colour, etc. The crimsons in Gothic tapestries must have been got by dyeing kermes over pale shades of blue, since the crimson red-dye, cochineal, had not yet come to Europe.

A word or two (entirely unscientific) about the processes of this old-fashioned or artistic dyeing.

In the first place, all dyes must be soluble colours, differing in this respect from pigments; most of which are insoluble, and are only very finely divided, as, e.g., ultramarine, umber, terre-verte.

Next, dyes may be divided into those which need a mordant and those which do not; or, as the old chemist Bancroft very conveniently expresses it, into adjective and substantive dyes.

Indigo is the great substantive dye: the indigo has to be de-oxidised and thereby made soluble, in which state it loses its blue colour in proportion as 205