PLATE-GLAZING 307
The mottled appearance of some papers is caused by bad damping— Le.9
insufficient time for penetration and spread of the water, or the damper throwing
drops instead of spray—cloudy or patchy make of the paper, or strong fibres
that will not make a close sheet. In the last case the mottled appearance is
sometimes looked for and desired, to show up a strong paper.
Paper intended for a high finish should be specially made for such if possible.
The stuff should be beaten so as to produce a close sheet, with the addition of
some good china clay and starch. On the machine full use must be made of
the shake, and a heavy dandy roll run. If finish is wanted to be. equal both
sides, the paper must be run through the second press and smoothing rolls
to eliminate wire, coucher and felt impressions.
Plate-Glazing.—K plate-glazed finish is applied only to high-class papers.
The plate-glazing calender is a machine consisting of a heavy frame carrying
two iron rolls. Just under the level of the nip are smooth metal plates, or
rollers, both at back and front. The action of the rolls is reversible and the
top roll is fitted with levers to apply pressure. The sheets of paper are placed
alternately with plates of copper, zinc or cardboard, until a pile, 'book', or
'handful', as it is called, is formed about iŁ to 2 inches thick.
The pile is laid on the metal platform or rollers and the rolls are started.
It is pushed into the nip and the rolls grip it and take it through on to the back
platform. On the rolls being reversed, the pile is pulled back through the nip.
It is then turned half round and the process repeated. The turning of the pile
is for the purpose of reducing the curl of the plates and paper and giving the
paper equal finish and expansion in the machine and cross directions.
The necessary amount of finish is obtained from the burnished surface of
the plates, the pressure and the number of times the pile is put through the
rolls. High finish is given by copper or zinc plates, low finish by cardboard.
One man works the machine, but it is sometimes necessary to have an assistant
turning the pile at the back for low finishes and helping to lift a heavy 'book'
from the bench. Women are employed to lay the sheets of paper and metal
and to separate them afterwards.
A plate-glazed finish is very fine and silky, and the most permanent of all
finishes. An extremely high glaze may be put on the paper, but if overdone
the sheet may be crushed out of all recognition. In any case, specks of dirt
are shown up very prominently. One may look through hundreds of sheets
without finding a single one that is faultless in this respect.
Unless trimmed, the edges of a plate-glazed sheet are slightly rougher than
the centre, owing to the difficulty of laying the paper and metal plates so that
all the edges coincide.
Plate-glazing is a very expensive method, owing to the labour and time