286 MODERN PAPER-MAKING
Tayer1 and piled into packs', which are taken and pressed again for some
hours. These packs are then separated sheet by sheet carefully, and then they
are pressed again for twelve hours, when they are again parted, pressed again,
and then hung up in a loft to be air-dried. In summer the natural air is enough,
but in winter steam-pipes are used. When sufficiently dry the paper is stacked
up in piles to mature and flatten out. This maturing process may take weeks
or months. The waterleaf is now ready to be sized with gelatine.
The sizing is carried out in a sizing machine, which consists of a tub through
which two endless felts travel slowly, with the sheets of waterleaf between
them* After the sheets have been well soaked they are carried between squeez-
ing; rolls to force the size into the sheets and also to remove excess size from
j^
the surface of the sheets; this prevents subsequent discoloration by reason of
patches of size lying on the surface.
After sizing, the sheets are stacked up in piles and covered with hot felt
and allowed to stand for about twenty-four hours. This gives the size a chance
to permeate the sheet thoroughly and the heat prevents the sheets sticking
together. After this the sheets are parted by girls, so that warm air can get
at them and dry off the surplus moisture.
The paper is afterwards allowed to stand in piles for a day and then again
carefully parted sheet by sheet, care being taken not to strain the sheets unduly
if they should be stuck together, otherwise they will be cockled and will never
lie flat.
The sheets are again allowed to stand for a few hours, and are then
taken to the drying lofts. These lofts are heated and care has to be taken to
prevent cold air or draughts getting in, or the paper will be spoilt. Different
temperatures are used for drying different qualities of paper. The paper may
be dried flat on hessian screens, or hung over cow-hair ropes. Most papers
are sized a second time after drying. The stronger the paper and the more
fibrillated the stock, the more difficult it is to get the paper to take the size,
owing to the absence of air spaces. After drying in the loft the paper is stacked
in heaps to mature, and is then sorted over for defective sheets before being
plate-glazed. It is then sorted over finally by experienced sorters, who separate
it into good, retree and broken.
The most important features of hand-made paper are its great strength and
its tendency to expand and contract equally in both directions after damping
and redrying.
The shake given by the vatman is in two directions, so that there is very
little difference in the tensile strength in the length and breadth of the sheet.
Machine-made paper shows a decided difference in strength and expansion in
the machine and cross directions.