III. Mineral or
pigment colours. I described experiments to illustrate what we mean by
monogenetic and polygenetic colours, and indicating that the monogenetic
colours are mainly included in the group of substantive colours, whilst
the polygenetic colours are mainly included in the adjective colours.
But I described also an illustration of Group III., the mineral or
pigment colours, by which we may argue that chromate of lead is a
polygenetic mineral colour, for, according to the treatment, we were
able to obtain either chrome yellow (neutral lead chromate) or chrome
orange (basic lead chromate). I also said there was a kind of borderland
whichever mode of classification be adopted. Thus, for example, there
are colours that are fixed on the fibre either directly like indigo, and
so are substantive, or they may be, and generally are, applied with a
mordant like the adjective and polygenetic colours; examples of these
are Coerulein, Alizarin Blue, and a few more. We have now before us a
vast territory, namely, that of the _b_ group of substantive colours,
or, the largest proportion, indeed almost all of those prepared from
coal-tar sources; Alizarin, also prepared from coal-tar, belongs to the
adjective colours.
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