SUPPORTS 245
a smooth, almost glazed surface. Several materials have been used for screens in
the shallow sieve that collects and felts paper fibres. In a few instances, the bottom
has been made of cloth. Fine reeds were generally the material used in the Far
East. In the West paper has been formed usually on wire screens, and papers made
on such a screen usually show, especially when held to the light, a faint pattern
of the screen which is called a * wire mark/ The marks are caused by the tendency
of the pulp to settle more between the wires than over them and so their positions
are faindy marked by an alternation in densities. Special characteristics in the
wire marks sometimes give a clue to the time and origin of the paper.
Water-marks, probably suggested by the screen marks or wire marks im-
pressed in paper during hand manufacture, are the initials, names, seals, or sym-
bols marked in Occidental paper by the same means. They are made by wires
which are set into the screen on which the sheet is formed. The wet pulp settles
out more thinly along the lines of the design made by these wires and the design
shows as somewhat more translucent than the sheet around it. Oriental papers
have no water-marks, nor have those of Arabian and European manufacture be-
fore the end of the XIII century. They first appear in the product of either the
mills of Bologna, 1285, or the mills of Fabriano in 1293 and 1294. Since then they
have been common and the history of them occupies many volumes (see Briquet,
in particular). In the XIV century they are characterized by simple designs and
large wires. For a short time (1307-1320) in Fabriano the maker's full name was
used, but the mills then went back to simple initials until the XVI century. By
1545 the date of manufacture began to be added to the full name of the maker.
Until about 1790 they were usually called ( paper-marks.*
When paper is made By machine, the wet pulp flows out on a moving, endless
mold of fine wire cloth. It is beaten, strained, cleaned, and carried to a screen of
brass cloth supported by tube rolls. This is forty to fifty feet long. As thin pulp it
goes over suction boxes and through rolls. Then, as paper, it is passed on felts
through other rolls that take out moisture and over heated cylinders for further
drying. The better papers are * tub-sized' with gelatin or animal glue, containing
alum, after they leave the drying cylinders.
The preparation of pulp from materials other than rags is somewhat more
complicated. When raw fibre is taken for paper-making, it is necessary to remove
as much as possible of intercellular material (see also Fibrous Substances). In the
case of esparto the grass is boiled at a high temperature, and for three or four hours,
in a strong solution of caustic soda. A steam pressure of thirty to forty pounds per
square inch is usually maintained. The fibres are drained, washed, and bleached,
intercellular matter being largely digested by the caustic soda. Roots and other
impurities are taken out of the pulp. A method similar to this is used for straw.
Mechanical wood-pulp is little more than sawdust matted into sheets. For
chemical pulp three methods of preparation have to be distinguished: the soda
process, the sulphate process, and the sulphite process. The soda process is used