soaking
1. The process of treating raw hides and skins
with water. The restoration of moisture lost
during curing and storage, as well as the removal
of extraneous matter are of prime importance in
converting raw stock into leather. The restoration
of moisture is essential because: 1) the stock may
otherwise be physically damaged by the action of
washing under agitation, and flexing during green
or lime fleshing; 2) sufficient moisture within
the stock is necessary for solution and
elimination of salts and globular proteins
contained within the fibrous hide structure: and
3) the replenished water serves as a diluent as
well as a vehicle for penetration into the fibrous
structure of the astringent chemicals employed to
effect hair loosening, plumping. and required
alkaline action. Removal of extraneous organic and
inorganic matter, except epidermis and flesh, by
soak-washing is essential because: 1) solid matter
in excessive amounts can result in both stock and
machine damage during fleshing a nd unhairing; 2)
manure and urine are ideal foods for bacterial
growth during soaking. (Such matter, along with
certain salts in the soaks, can result in
discoloration and stains on the stock that cannot
subsequently be removed): 3) the cementing effect
of globular proteins upon dried tanned fibers
reduces fiber mobility necessary for softness and
good handle in the final leather; 4) curing salts
transferred to the lime liquors affect the
alkaline plumping action, reduce the rate of
unhairing, and cause a contraction of the grain
surface of the stock; and 5) the presence of
extraneous matter presents a false and variable
hide substance weight in determining the amounts
of materials required for liming.
Because of many variable conditions. the time and
temperature of soaking varies considerably
according to the kind of stock being treated.
Generally, few soaking aids are used in soaking
cured and brined stock unless a considerable
number of a given lot have been stored under
exceptionally dry and warm conditions. In such
cases. either sodium sulfide (63%) or sodium
hydroxide may be used to the extent of 1.0 to 0.S
pound respectively per 100 gallons of water. These
chemicals are frequently employed in the soaking
of dry stock. Excessive amounts will cause a high
grain in the leather.
2. The process of wetting the grain side of a
leather with water and the flesh side with paste
to improve the pliability of the leather
preparatory to covering. (161 , 248 , 291 , 298 , 306 , 363 )
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