ioo MODERN PAPER-MAKING
a ledger paper of 72 Ib. Imperial, we have to beat with less fibrillation. This
is not because we do not require strength, but because we find it very difficult
to get the water out of the fibrillated stuff when we run it over the wire. There-
fore the beating is required to be a very skilful compromise between cutting
and fibrillating the fibres. We must not cut them too short or strength will
be badly down; we cannot leave them long and raw or we will have trouble
in getting them through the strainer plates and get a poor water-mark. In
general, with a fair quality of cotton fibres, if we treat them as for a ledger
paper of about 30 Ib. in Large Post, by heating the stuff to about 90° to 95° F.
on the machine, a successful result will be achieved.
With substances heavier than this, strength has to be proportionally sacri-
ficed to the capacity of the machine to extract water, and the fineness of the
strainer slits. A good cotton furnish beaten for i hour with sharp plates may
be run up to 150 Ib. Imperial on a 40-foot wire of 66 mesh at 15 to 20 feet
per minute without heating at the machine. Heating up to 90° to 100° R
allows the stuff to be put down with a little more length, as more water can
be used to run it through the strainers.
When dealing with cotton fibres from old rags, more gentle treatment is
necessary. Fibres that have been subjected to prolonged wear and repeated
washing and bleaching before coming to the mill, and then to a fairly drastic
treatment there, have lost a great deal of their stability and bulk, and—worse
still—have become partly oxidised. Fewer twisted fibres are seen, and the most
careful beating cannot make up for the loss of their original strength. They
are also frayed apd bruised (i.e. fibrillated), and therefore work wetter on the
machine. They serve to make rag papers that may be sold comparatively
cheaply and fulfil a more modest standard of quality, and they form the basis of
the great majority of writing and ledger papers.
Old soft rags, suitably treated and beaten with very sharp roll bars and
plates, make the softest and most absorbent blottings. The beating time is
from i to 3 hours, according to substance. Blotting Demy (17^x22) varies
from 18 to 120 Ib.
Owing to its absorbency and the purity of its fibres, cotton takes most
dyes very readily and produces very brilliant shades.
Cotton fibres blend extremely well with the fibres of chemical wood, and
very beautiful and useful papers of all types, from the thinnest banks to the
thickest chromos, may be made from a mixture of the two.
The strongest form of cotton rag is that known as 'new unbleached calico
cutting^ from doth which has "been woven from Egyptian cotton. The half
stuff from this material bleaches up to a beautiful snowy white and may be
beaten to yield very strong papers of all substances.