The liming of goatskins presents some points of contrast with the
methods used for other skins. These differences are due to the
exceedingly tight and compact nature of the skin fibres. This
compactness of texture makes it quite necessary to dissolve the
interfibrillar substance to a greater extent than usual, and also to
plump the fibres and split them into the constituent fibrils. These
effects are essential to obtain a rapid and complete tannage and a soft
leather. Too much bacterial action should be avoided, however, or the
brightness and soundness of the grain may be impaired, which would be a
fatal defect in such a leather. Hence the liming is long rather than
mellow, and sharp limes rather similar to those required for sole
leather are often used. Another result of the tight texture of goatskin
is that depilation is not easily effected. This feature is rather
intensified by the deepness of the hair-root. Hence it is usual to
employ sulphides to assist the depilation. In one method two rounds of
five pits are used. The skins are given about two days in each pit, so
that the liming lasts approximately three weeks. In the first round,
which consists of rather mellow limes, arsenic sulphide is used to
assist depilation. Up to 6 per cent. on the weight of lime is added
during slaking. This is a comparatively large amount of arsenic
sulphide, and the depilation is considerably hastened; the skins indeed
are unhaired after passing through this round, _i.e._ after about 10
days' liming. In the next round the object is plumping, and caustic soda
(or carbonate) is added to the lime liquors in quantities comparable to
those suggested for sole leather (Part I., Section V.). In
this round the goods stay also for about 10 days. An alternative to the
above process is to hasten the earlier part of the liming by employing
sodium sulphide instead of realgar. More sulphydrate may be obtained in
solution in this way, and the unhairing may be in about half the time.
The sulphide of soda also commences the plumping action which follows in
the next round, but this alternative has the disadvantage that the skins
are unhaired whilst the pelt is swollen with sulphide, which renders the
grain both harsh and tender and consequently more liable to damage by
the unhairer's knife.
Public-domain text, read in full here on John Shaqi.
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