Calico-printing is executed either by hand (with wooden blocks having
the pattern engraved--projecting--on their surfaces) or by means of
machinery. Printing by hand-blocks is a tedious operation, and is now
almost superseded by the cylinder. The hand process is very similar
to that made use of in paper-staining (which see). Cylinder-printing
is a much more rapid process, conducted by means of a brass cylinder
with the pattern engraved on its surface, which is made to revolve
against another cylinder covered with flannel, and charged with color
from a trough into which its lower part is dipped. The calico is
passed over a large cylinder made to revolve in contact with that on
which the pattern is engraved, and which is charged with color from
the one below it. Fig. 1 shows this arrangement, _a_ being the large
cylinder with the calico round it, _b_ the engraved cylinder, _c_ the
color cylinder, and _d_ the color trough. As the engraved cylinder
revolves, it prints the pattern at each revolution, and this is
repeated again and again, to the whole length of the piece of calico.
In some machines there are several engraved cylinders, each printing
its own color, and so arranged that the colors shall fit into the
parts of the design requiring them, the whole making up the complete
pattern.
Illustration: AGEING PROCESS.
Illustration: DRYING ROOM.
Before being printed, the calico is prepared by being passed through
a preparation, called a mordant, capable of fixing the colors, and
preventing them being washed out, and several of these are used,
according to the colors required. The colors are thickened with
paste, so as to prevent them from running into each other when
printed. Muslins, chintzes, &c., are printed in a similar manner to
calicoes.
When the pieces of calico come from the printing cylinders, they are
made to pass upwards through holes in the ceiling to a room above,
where they pass over surfaces of iron heated by steam, so as to
thoroughly dry them; they then descend through the floor into the
printing room, where they are packed. The process called “ageing”
consists in exposing the calicoes to the air for a certain time,
to take off the harshness and stiffness peculiar to new goods.
In some cases the colors themselves are not printed on the goods, the
mordants being used instead, and the whole piece is then boiled in a
vat of dye-stuff, which, however, only adheres to the parts printed
with the mordant, all the rest being easily got rid of by simple
washing.