CURRYING.
In general terms, the process of currying consists in softening,
levelling, and stretching the hides and skins which are required for
the upper-leathers of boots, and other purposes demanding flexibility
and softness, and in saturating or "stuffing" them with fatty matters,
not only in order to soften them, but to make them watertight, and to
give them an attractive appearance.
It is obvious that great differences must be made in the currying
process, according to the character of the skin and the purpose for
which it is intended, since the preparation of French calf for a light
boot, and of the heaviest leather for machine belting, equally lie
within the domain of currying. In this case, however, as in that of
tanning, the clearest idea of the general principles involved will
be gained by taking a typical case, and afterwards pointing out the
different modifications needed for other varieties. The French method
of currying waxed calf is selected as an example, since the well-known
excellence of this leather makes it interesting to compare the details
with the methods ordinarily in use in this country.
After raising the skins from the pits, and beating off the loose tan,
they are hung in the sheds till partially dry (_essorage_), great
care being taken that the drying is uniform over the whole skin. In
modern shops, this drying is usually accomplished at once, and in a
very satisfactory manner, by means of a hydraulic press. If dried in
the air, they must be laid in pile for a short time to equalise the
moisture, and then brushed over on flesh and grain. The next process
consists in paring off loose flesh and inequalities (_dérayage_).
This is done on a beam, and with a knife similar to that used in
bate-shaving, and shown in A, Fig. 26. This knife has the edge turned
by rubbing with a strong steel, and is called _couteau à revers_.
Next follows the _mise au vent_. The skins are first placed in a tub
with water or weak tan-liquor for 24 hours; they are then folded and
placed in a tub with enough water to cover them, and beaten with wooden
pestles for 1/4 hour. At the present day, stocks (_foulon vertical_),
or a "drum-tumbler" (_tonneau à fouler_), a machine on the principle
of the barrel-churn, usually take the place of this hand-labour. The
skin is next placed on a marble table, flesh upwards, and with one
flank hanging somewhat over the edge, and is worked with a "sleeker" or
stretching-iron (_étire_), B, Fig. 26. The first 2 strokes are given
down and up the back, to make the skin adhere to the table, and it is
then worked out regularly all round the side on the table, so as to
stretch and level it. The flesh is then washed over with a grass-brush
(_brosse à chien-dent_), the skin is turned, and the other flank is
treated in the same way. It is lastly folded in 4, and steeped again
in water. The next process is the cleansing of the grain. The skin is
spread again on the table, as before, but grain upwards, and is worked
over with a stone (_cœurse_), set in handles, and ground to a very
obtuse edge. This scours out the bloom; after washing the grain with
the grass-brush, it is followed by the sleeking-iron, as on the flesh.
The next step is resetting (_retenage_). For this, except in summer,
the skins must be dried again, either by press or in the shed. This is
another setting out with the sleeker, and, the skin being dried, it
now retains the smoothness and extension which is thus given to it.
The skins are now ready for oiling in the grain, for which whale-oil
or cod-liver oil is generally employed. Olive-oil, castor-oil, and
even linseed-oil may, however, be used, and are sometimes made into an
emulsion with neutral soap and water. After oiling the grain, the skins
are folded and allowed to lie for 2-3 days before oiling the flesh.
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.]
[Illustration: Fig. 55.]
The Fitzhenry machine has also been constructed so as to work in any
direction over a fixed table, being driven by a small direct-acting
steam-cylinder supplied by jointed pipes. But probably the most perfect
scouring and setting machine which has yet been introduced is the
Lockwood Automatic Scourer, which may also be regarded as a development
of the Fitzhenry machine. This has been some years in use in America
with great success, and has received considerable improvements, but has
only very recently been introduced into England by Messrs. Schrader and
Mitchell of Glasgow, who have kindly furnished the annexed illustration
(Fig. 56). In this machine the table is fixed, and the tool-carriage
can be moved over it in every direction. The large projecting carriage,
or cross-head, which supports it, travels on a horizontal rail, which
may be observed below and behind the table. Motion is given to it by a
screw which is driven in either direction by the pulleys at each side
of the cross-head. In a similar way the tool-carriage is traversed
forwards or backwards by a second screw at right angles to the first,
and by a most ingenious interlocking arrangement both screws are
controlled by a single handle. The tool-carriage or "trundle frame"
can also be turned like a turntable, so as to deliver its stroke in
any direction, the tool-holder being driven by a horizontal crank
in the centre of the frame, and immediately above the tools. Though
the machine is complicated, and necessarily expensive, it has not been
found either in America or Scotland difficult to work or liable to
get out of order, while both the quantity and quality of its work are
all that can be desired. Fig. 55 is Gläser's scouring machine. Fig.
57 illustrates the latest English scouring machine, Messrs. Haley and
Co.'s Climax Scourer, which is also ingenious and effective. In it the
table instead of the tool-holder is movable by screws driven by belts
thrown into gear by a handle, and it is provided with two tables of
which one is in work while the hides are being changed and spread on
the other. The oscillating tool-holder, instead of being actuated by
the rise and fall of the connecting-rod, is moved by an adjustable
eccentric.
[Illustration: Fig. 56.]
[Illustration: Fig. 57.]
In the case of strap-butts, the currying is, of course, far less
elaborate. They are well scoured out, heavily stuffed, and stretched in
screw-frames, to prevent their giving afterwards when in use.
In Germany, Switzerland, and Austria, a method of stuffing strap-butts
is frequently employed, which, so far as I am aware, is not in use in
England. It is called _Einbrennen_ or "burning in," and consists in
applying very hot tallow to the dry leather. The butts are washed free
from liquor in a tumbler, boarded to soften them thoroughly, scoured,
set out with a sleeker, nailed on laths, and air-dried. They are then
very completely dried in a room heated to 104°-113° F. (40°-45° C.),
as if any moisture remains in the hide, the fibre will be destroyed by
the heat of the melted tallow. The tallowing generally takes place in
the same room, as a high temperature is required to allow it to soak
in, and the leather would greedily reabsorb moisture if exposed to
damp air. The tallow is heated, generally by steam in a jacketed pan,
to 167°-212° F. (75°-100° C.). There are two ways of applying it. The
melted tallow may be applied on a table to the flesh side of the butt
with a ladle, and rubbed on with a brush or rag. In this case, as soon
as the tallow has sufficiently soaked in, the butts are placed in water
to prevent its striking through to the grain. The second way is to
have the pan of sufficient size and suitable shape, and for two men to
draw the butt through the melted tallow with tongs, and more or less
rapidly according to the quantity it is desired that the leather should
absorb; and in some cases the process is repeated once or more. In this
case, it is useless to wet in water, and the butts are allowed to cool
gradually in pile.
The leather is now impregnated with grease, but it is far from being
properly stuffed. Instead of the grease being spread over the finest
fibres in a minute state of division, it simply fills the spaces
between the larger fibres. To remedy this, the butts are well softened
in water (which, if they have been drawn through the tallow and allowed
to cool, must be tepid), and are then worked in a damp condition in a
drum tumbler, by which they brighten in colour and become uniformly
stuffed. They are then allowed to lie in a pile a day or two, are
stoned and worked out with the sleeker, and hung up to dry. When in
right temper they receive a final setting out with the sleeker, and
when dry are either rolled or glassed. For further details, Nos.
256 and 257 of 'Der Gerber,' 1885, must be consulted, where the
matter has been exhaustively treated by Eitner, in his papers on
"Extract-Gerberei."
[Illustration: Fig. 58.]
In England, curried leathers are generally sold by weight, which
leads to the use of glucose and other materials to add to the weight.
In America, all upper leathers are sold by measure, and this is
now ascertained by a very ingenious machine (Fig. 58). The skin is
laid on a latticed table, and a frame, from which rows of bullets
are suspended, is let down upon it. The total weight of the frame
is indicated by a spring balance, and as the bullets which are over
the skin are supported by it, the diminution of weight indicates the
measurement. Several modified forms of this machine are now made.