CHAPTER X
DYEING OF PAPER-MINERAL AND INORGANIC DYES-THE
USE OF ANILINE DYES
Dyeing of Paper.—The colouring of paper to shade is the most baffling
process in paper-making. It is intricately connected with quality, beating and
making. By quality we mean not only difference in fibres as between, say,
cotton and esparto, but any difference in quality of the same fibres. No two
consignments of fines, seconds or other kinds of cotton rags are ever so much
alike as to produce identically similar fibres. All other paper-making materials
are subject, more or less, to variations, both in the condition in which they
come to the mill and in their subsequent treatment there. For example, wood
pulp, which is the most regular of all supplies of fibre when obtained from the
same source and of the same brand, will be found to vary in colour, strength
and purity. This may be from causes quite beyond the maker's control, such
as the condition of their raw materials, the logs from the forest, the chemicals
they use to reduce the wood to fibres, their water supply and many other
causes, some of which are known and guarded against as far as possible, while'
others are still matters of mystery. The paper-maker knows this, and if the
variations are not great, he has to accept the supply and make the best he can of
it. Unfortunately, he does not find die paper consumer quite so complacent,
and must direct all his skill to eliminate these differences and make up deficiencies
in colour, quality and strength by any means he can devise.
Rags are by far the most variable of raw materials, and unless great care
is taken in their mill treatment, the resulting half stuffs may have extreme
differences in quality. Apart from other things, colour will be the greatest
difficulty. Suppose a high-grade writing paper is being made from fines, and
the natural white colour of the bleached rags gives the correct shade to a standard
sample. The next making from a different lot of rags may be dull or yellow
compared to the first The paper-maker may try to match his sample by
tinting the stock with blue, or blue and pink. A fair match may be obtained,
but careful examination in comparison with the previous making will show it
to look 'coloured' instead of pure white. Then he may have to alter his
furnish to get the desired tint by adding a certain percentage of white rags,
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