It cannot be dyed either
by English or German methods; neither logwood black nor coal-tar blacks
can make any really good impression on it. Cases have often been
described to me illustrating the difficulty in preventing hats which
have been dyed black with logwood, and which are at first a handsome
deep black, becoming rather too soon of a rusty or brownish shade. Now
my belief is that two causes may be found for this deterioration. One is
the unscientific method adopted in many works of using the same bath
practically for about a month together without complete renewal. During
this time a large quantity of a muddy precipitate accumulates, rich in
hydrated oxide of iron or basic iron salts of an insoluble kind. This
mud amounts to no less than 25 per cent. of the weight of the copperas
used. From time to time carbonate of ammonia is added to the bath, as it
is said to throw up "dirt." The stuff or "dirt," chiefly an ochre-like
mass stained black with the dye, and rich in iron and carbonate of iron,
is skimmed off, and fresh verdigris and copperas added with another lot
of hat-forms.
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