DYEING 133
with ultramarine blue, it turns the latter to a greenish shade and reduces the
brightness of too brilliant colours. The yellow shade is permanent and tends
to deepen with age. It is very valuable for toning down mixed furnishes, as it
acts on most fibres equally well, and does not produce the mottled appearance
which is caused by toning with aniline yellow.
Carmine or Cochineal Paste is the only colour of its kind, being made from
the bodies of cochineal insects, which are parasites of the prickly pear. While
not so powerful as the brilliant pinks of the aniline class, it is peculiarly adapted
for dyeing high-class papers, owing to the ease of its manipulation and its
purity. It requires to be treated with ammonia and cream of tartar (12 Ib. of
paste, 2\ pints of liquid ammonia, 2 oz. of cream of tartar), and allowed to
stand for a week or two to mature. It is very fugitive and is seldom used alone,
being chiefly of value in combination with ultramarine for shades of white,
high-class papers.
ANILINE COLOURS
These are produced by intricate chemical processes from coal tar in prac-
tically every colour and shade. They are of acid, basic or neutral character,
but all are fairly easy to manipulate and are fixed by alum. They are absorbed
by the fibres, but are mostly very fugitive and susceptible to light. They
require to be dissolved in very hot water, and carefully strained to prevent
specks of undissolved colour showing in the paper. When combinations of
aniline colours are used, acid and basic colours will precipitate each other in
the fibres and help to reduce the waste in the back water. They are used for
very brilliant shades, alone and with natural colours. They dye mechanical
pulp very well and more cheaply than mineral dyes. They are very useful
for blottings and other special papers where alum is inadmissible.
Within the last few years some very permanent dyes of this type have been
discovered, and it seems likely that in course of time the old-fashioned mineral
colours will be superseded by the modern products. It is hardly necessary to
give any list of aniline dyes. The leading manufacturers will supply catalogues
of their products and send samples for trial; also, they will, on request, match
a sample and supply all particulars as to quantities and treatment.
PMOICAL NOTES ON THE USE OF ANILINE DYES
- Before fibrous materials can be effectively and economically coloured widi
synthetic dyes, the nature of the fibres and dyes has to be considered in idbtkm
to their suitability. Certain dyes are said to have an affinity for certain fibres,