SOLE-LEATHER.--Treatment in the Shed.
[Illustration: Fig. 44.]
The butts, after being treated as above described, are frequently oiled
lightly on the grain, and are taken into the drying-lofts, where they
are hung on poles till about half dry. They are then laid on the floor
in piles, and covered up till they heat or "sweat" a little, which
facilitates the succeeding operation of "striking." This is performed
by laying the butt over a horizontal "beam" or "horse," and scraping
its surface with a triangular pin, shown at D in Fig. 25. This pin has
an even, though tolerably sharp, edge, and is so used that it stretches
and smooths out the grain, without breaking it; and at the same time
it removes a portion of the white deposit called "bloom," which has
been mentioned. Common goods are frequently struck by the machine
introduced by Priestman, of Preston Brook, shown in Fig. 44; but the
work is not very uniform, and the leather is much compressed and
stretched. For offal, the machine is a very useful one, and perfectly
satisfactory.
[Illustration: Fig. 45.]
[Illustration: Fig. 46.]
Butts are now generally struck by the very ingenious machine of
Wilson, whose name has also been mentioned in connection with the
disintegrator, and which is shown in Fig. 45. The arms carry blunt
brass or steel knives or sleekers, and work outwards from the centre,
while the butt is carried backwards and forwards over the drum. Stones
may be substituted for the sleekers, when it is required to remove the
bloom. The machine requires a firm foundation, as its reciprocating
motion causes considerable vibration.
[Illustration: Fig. 47.]
After a light oiling and a little further drying, the butt is laid on
a flat "bed" of wood or zinc, and is rolled with a brass roller loaded
with heavy weights. Various machines are also in use for this purpose.
In Fig. 46, is shown Wilson's spring butt-roller, in which the pressure
is produced by springs immediately above the roller, which works
backward and forward over a flat table, beneath a fixed girder. In the
later patterns of this machine the roller is automatically reversed
by a mechanical finger before coming to the edge of the butt. Fig. 47
shows an adaptation of the American pendulum roller, which is specially
suited for refinishing Singapore kip sides and the commoner class of
goods, giving great firmness and a high gloss. Fig. 48 represents a
machine in which the roller is fixed, and works over a brass drum; it
is specially adapted for offal, and, when used for butts, is apt to
make them "baggy." In this machine, the reversing motion is obtained by
using two belts, one being crossed.
[Illustration: Fig. 48.]
The leather is now frequently coloured on the grain with a mixture,
for which each tanner has a recipe of his own, but usually consisting
mainly of yellow ochre with size or liquor and oil in order to give
a gloss, and to hide uneven or dull colour, and, when sufficiently
dry, is well brushed by hand or power, rolled a second time, and
dried-off in a room gently heated by steam. This is the Bristol method
of finishing. In the Lancashire district, butts are generally struck
out much wetter, and "stoned," so as to remove the whole of the bloom,
and show the natural brown "bottom" of the grain. When sufficiently
dry, they are struck a second time, to set the grain, and rolled as
described, the painting being omitted. This method has the disadvantage
of requiring more labour, and causing a loss of weight; but leather so
got up brings a higher price, as the finish is only applicable to such
tannages as make a fair colour. The usual London plan is a compromise
between the Bristol and Lancashire methods; the leather is sammed, or
tempered by partial drying and piling before striking; stoning is not
resorted to, but the bloom is thoroughly removed from the surface with
the pin and scrubbing-brush. Colour is not generally used.
It is very important, and especially so with heavy mixed tannages,
that the drying should be conducted in the dark, and not too rapidly.
No artificial heat should be used, except in frosty weather, to wet
leather; and it should be carefully protected from harsh drying
winds. After the leather is finished, it should be dried off in a
well-ventilated drying-shed, heated to about 70° F. (21° C.). The same
observations apply to the drying of rough dressing-leather, except that
artificial heat should be avoided. Frost makes dressing-leather porous,
and prevents it carrying a proper quantity of grease in currying. On
the construction of drying-sheds, see pp. 243-54.