Other experiments have shown
that the chromium and iron logwood blacks hold an intermediate
position. Abnormal properties are found to be exhibited by camwood and
its allies, with aluminum and tin, the colors at first becoming
darker, and only afterward fading in the normal manner.
When we examine the silk patterns, we find, generally speaking, a
similar degree of fastness among the various natural dyes, as with
wool; in some instances the colors appear even faster, notice, for
example, the catechu brown and the colors given by brazilwood and its
allies, with iron mordant.
On examining the cotton patterns, we are at once struck with the
marked fugitive character of nearly all the natural dyes. The
exceptions are: the madder colors, especially when fixed on
oil-prepared cotton, as in Turkey red; the black produced by logwood,
tannin, and iron; and a few mineral colors, e.g., iron buff, manganese
brown, chromate of lead orange, etc., and Prussian blue. Cochineal and
its allies, which are such excellent dyes for wool and silk, give only
fugitive colors on cotton.
The main point which arrests our attention in connection with the
natural dyes seems to me to be the comparatively limited number of
fast colors.
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