We may consider
them as colour-giving principles, and so we term them _polygenetic_
colours. Polygenetic means capable of generating several or many. In the
various colours and dyes we have all phases, and the monogenetic shades
almost imperceptibly into the polygenetic. The mode of application of
the two classes of colours is, of course, in each case quite essentially
different, for in the case of the monogenetic class the idea is mainly
either to dye at once and directly upon, the unprepared fibre, or having
subjected the fabric to a previous preparation with a metallic or other
solution, to fix directly the one colour on that fabric, on which,
without such preparation, it would be loose. In the case of the
polygenetic class, the idea is necessarily twofold. The dyeing materials
are not colours, only colour generators. Hence in all cases the fabric
must be prepared with the twofold purpose--first, of using a metallic or
other agent, capable of yielding, with the dye material, the desired
colour; and secondly, of yielding it on the fibre in an insoluble and
permanent form.
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