A Text-book of Tanning: A treatise on the conversion of skins into leather, both practical and theoretical.Procter, H. R. (Henry Richardson)
Science
A Text-book of Tanning: A treatise on the conversion of skins into leather, both practical and theoretical.
Procter, H. R. (Henry Richardson)
Tanning
The oiling on the flesh is done with a mixture of _dégras_ and tallow,
in such proportions as not to run off during the drying. _Dégras_ is
the surplus oil from the chamois-leather manufacture, which in France
is effected by daily stocking the skins with oil, and hanging in the
air for oxidation. The _dégras_ (_toise_, _moëllon_) is obtained,
not by washing the skins in an alkaline lye, as in the English and
German method, but by simple pressing or wringing. This oil, altered
by oxidation, is so valuable for currying purposes that skins are
frequently worked simply for its production, being oiled and squeezed
again and again till not a rag is left. It is generally mixed in
commerce with more or less of ordinary fish-oil. Eitner recommends,
where the _dégras_ is of indifferent quality, a mixture of 65 parts
_dégras_, 20 of neutral soap (i. e. soap without the usual excess
of alkali), and 15 of soft tallow. After oiling the flesh, which
is accomplished by extending the skin on the marble table with the
sleeker, and applying grease with a sheep-skin pad, it is hung to dry
at a temperature of 65°-70° F. (18°-21° C.). After drying, the surplus
oil is removed by a fine sleeker from both flesh and grain, and the
skins are ready for "whitening" (_blanchissage_). This consists in
taking a thin shaving off the flesh, and was originally accomplished
by the shaving-knife on the currier's beam, and some curriers are
still in favour of this method. It is now, however, usually done
by a sleeker with a turned edge. The grain then undergoes a final
stoning and sleeking, to remove the last traces of adhering oil, and
the skin is grained by rubbing it in a peculiar way under a pommel
covered with cork. It is then coated on the flesh with a mixture, of
which the following is a specimen:--5 parts of lamp-black are rubbed
with 4 of linseed-oil, and 35 parts of fish-oil are added; 15 parts
of tallow and 3 of wax are melted together and added to the mixture;
and, after cooling, 3 parts of treacle. This compound is put on with a
brush, and allowed to dry for some days. Finally, the skins are sized
over with a glue-size, which is sometimes darkened by the addition of
aniline-black.
The preceding account will give some idea of the care and labour
expended on these goods in France. In England, cheaper productions are
more in vogue, and almost every process is accomplished by machinery.
An illustration of the Fitzhenry or Jackson scouring-machine, which is
largely employed both for scouring and setting out, is given in Fig.
53. This is a simple and efficient machine, and has been largely used,
both here and in America.
[Illustration: Fig. 53.]
Fig. 54 shows the improved tool-carriage introduced by C. Holmes of
Boston, in which the brush and sleekers or stones are controlled by
handles which are stationary instead of moving rapidly with the slide,
as in the older form. Spiral springs are also substituted for the older
elliptical ones.
[Illustration: Fig. 54.]
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