The case is just the same with logwood black dyeing: without the
presence of iron ("copperas," etc.), sulphate of copper ("bluestone"),
or bichrome, you would get no black at all. We will now try similar
experiments with woollen fabrics, taking three simple pieces of flannel,
and also two pieces, the one having been first treated with a hot
solution of alum and cream of tartar, and the other with copperas or
sulphate of iron solution, and then washed. Turmeric dyes the first
yellow, like it did the cotton. Magenta, however, permanently dyes the
woollen as it did not the cotton. Alizarin only stains the untreated
woollen, whilst the piece treated with alumina is dyed red, and that
with iron, purple. If, however, the pieces treated with iron and alumina
had been dyed in the Magenta solution, only one colour would have been
the result, and that a Magenta-red in each case. Here we have, as proved
by our experiments, two distinct classes of colouring matters. The one
class comprises those which are of themselves the actual colour.
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