Deliming is by puering and drenching, and is often associated with a
further mechanical working of the goods. The skins are inserted into a
puer liquor at 85° F. and thoroughly pulled down. The caustic alkalies
should be completely neutralized. A slight cut into a thick part at the
butt end should develop no pink colour with phenolphthalein. The skins
should be thoroughly relaxed, and the swelling so much eliminated that
they are quite soft, weak and "fallen." The resilience and elasticity of
the plumped skins should have quite disappeared, and the impressions of
hand or thumb should be readily retained by the pelt. The grain should
appear white and possess a soft and silky feel. In this condition they
are again worked over the beam to soften further if possible. They are
then rinsed and again worked over the beam. Drenching follows with 10
per cent. of bran on the pelt weight, the operation commencing at 85° to
95° F., and lasting till next morning. The skins are next scudded
thoroughly to remove all dirt, but carefully so as not to damage the
grain.
In tanning, sumach and oak bark are the staple materials. Sumach gives a
much lighter colour, and hence it is used alone for goods that are to be
dyed the lighter shades, but oak bark is a "faster" tannage and more
preferable for dyeing in those cases where blacks and very dark shades
are wanted. For ordinary purposes a blend is usually employed. A feature
of oak bark, also, is that it tends to make a firmer leather, so that
the proportion used must be adjusted with this fact in mind as well as
the question of colour. For firmer moroccos the skins may pass through a
handler round of oak-bark liquors (10°-20°) in which a certain amount of
sumach is added to the liquors. The sumach is leached and assists both
in tanning and bleaching as the liquor works through the round. The old
liquor is run to a paddle, and the tannage is commenced by paddling the
drenched skins in this liquor. It is advantageous both for the tannage
and for the efficient "spending" of the sumach if this liquor be
slightly warmed. In the early pit liquors the goods are very frequently
handled. There is, however, the usual tendency of the times to save
labour in this direction, and hence it is common to have several paddles
with liquors of gradually increasing strength, followed by a shorter
round of handlers in which the handling is more infrequent. Instead of
paddles latticed drums may be inserted into pits containing liquors.
These, however, are not quite so convenient. In some tanneries,
especially where sumach only is employed, the tannage is in paddles
throughout. A new liquor is made up with fresh sumach and is used
repeatedly until exhausted. A three-paddle system sometimes obtains, in
which case the operation closely resembles the three-pit system of
liming (Part I., Section II.), and the skins pass through an "old"
liquor, a "medium" liquor and a "fresh" liquor. The goods need not be
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