pickling
The process in leather manufacture of bringing
hides and skins into a condition of equilibrium in
preparation for tannage. Pickling, which is a
process developed specifically for use in modern
chrome tannages, takes place following LIMING ,UNHAIRING , and DELIMING (and BATING ), and is used
particularly in the case of sheepskins. The skins
are de-wooled (the wool being more valuable than
the skins) and are then pickled, drained and
packed, ready for transportation to the tannery.
Pickling takes place in a solution of 12% salt and
1.2% sulfuric acid (previously diluted with
water). The salt solution should remain above 10%
and the acid above 0.8%. Furthermore, if the
proportion of salt to acid is incorrect the skins
may be damaged; consequently, both must be
carefully controlled. Pickled skins also must not
be allowed to become dry, as drying may cause the
acid to weaken the skin structure, and the
crystallization of salt on, or in, the grain may
lead to SALT
SPROUT .
The salt serves to preserve the skin, just as in
the case of salting for the purpose of curing,
while the acidity, if below a pH of 2.0, inhibits
nearly all known putrefying bacteria. The treated
skins, therefore, may be stored for several
months, provided they are kept cool; however, at
temperatures above 32° C., the acidity may
cause damage to the skins. Pickling, while
stopping bacterial damage, does not stop the
formation of molds, which favor pH values of less
than 5.0, and which can cause green, black, or
white discolorations, as well as a loss of gloss
or face on the finished leather. This is due to
their attack on the grain structure, and often
manifests itself in uneven dyeing. Mold growth can
be prevented by the use of fungicides added to the
pickle liquor in a concentration of about 0.001%
of the weight of the liquor. A typical pickle
fungicide is paranitrophenol. (248 , 306 , 363 )
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