Bourne Archive:
Muspratt: Speciality Leathers
http://boar.org.uk/aaiwxw3MusprattL8Fancy.htm Latest edit 27
Dec 2010
The Bourne Archive
Muspratt’s Chemistry, Theoretical,
Practical & Analytical (ca. 1859)
Extracts Concerning Leather, 9: Fancy and
Speciality Leathers.
The web pages linked
from this introduction are from an article on tanning, under the heading
‘Leather’. The original article is presented here in several web pages,
respectively dealing: 1,
with leather; 2,
with tanning materials; 3, Sources of
tannin; 4, crushing
mills; 5, varieties
of skin; 6, hide
preparation; 7, the
common tanning process; 8, finishing
processes; 9, fancy and speciality leathers.
Vol. 2. pp. 524-532
Fancy Leathers.—Besides the various kinds of
leather already described, there are many others, included under the heading of
fancy leathers, which are extensively
used, and are therefore manufactured on a large scale. Such are the well-known
Russian leather, morocco, Hungarian,
and chamois leathers, with a few others of lesser importance, but which,
nevertheless, merit a short description.
Russian Leather.—This article, known as jucten, has long been valued for its
qualities of resisting moisture and the ravages of insects, as well as by the
peculiar odor it possesses—qualities which render it of great importance to
book-binders and others.
The method of preparing this article, is not very
generally known out of the seats of the manufacture, but the following details
from the memoir of Count de Kartsoff
on the subject will give an insight into the process:—The dried skins are
softened by soaking in water for five or six days in summer, and ten or twelve
in winter; well cleaned and deprived of their hair by the use of milk-of-lime,
prepared by disseminating one hundred and eighty-five pounds in a vat or tub
eight feet in diameter, and seven feet three inches deep, nearly filled with
water. During the steeping the skins were frequently examined, and as soon as
the hair and epidermis are found to be detached, they are worked upon the beam
with a dull knife, and afterwards with a sharper instrument, on the flesh side,
to separate extraneous matter. When ox and cow hides are operated upon, the
depilation is effected by piling them one upon another, sprinkling some common
salt upon them to resist the injurious effects of over-fermentation, and after
the proper time, has been allowed, working on the beam as before. Bran-water
baths are occasionally resorted to for the same purpose, but only when the more
delicate skins are treated.
The usual steeping and beating, et cetera, are given after the depilation, with a view of removing
the lime; and after this is done, the cleaned pelts are introduced into a vat
like that described, containing a fermented menstruum 1 of eleven hundred pounds of rye, and
four hundred and fifty of oatmeal, six pounds of salt, and a sufficient
quantity of leaven. They remain here for forty-eight hours or longer, according
to circumstances, in which time they become raised.
The tanning process is then commenced by steeping them for some time in a weak
infusion of oak or willow bark by preference. After this the skins are placed
in a tan-pit, interstratified with layers of coarse willow bark till it is
full, and then charged with the liquor of the last steep, the whole being
pressed by planks and stones. Fifteen to twenty-eight days are allowed to
transpire before they are disturbed; at the end of this period the pit is
emptied, fresh bark and solution substituted for the exhausted material, and
the whole left as before. Three to six such changes and terms are required,
according to the thickness and weight of the skins, to finish the tanning; very
thin skins get but two changes. Whilst tanning, the leather acquires rigidity,
which is removed by immersion for a day or longer in a thin paste made of one
hundred and thirty pounds of oatmeal, and nine of salt, macerated 2 with warm water. This quantity should
serve for one hundred and fifty skins of ordinary size. When taken out of this
steep, the leather is well cleaned, and allowed to drain. At this juncture the
currying commences, which confers the particular virtues already mentioned. The
leather still moist, but not over-saturated, is placed with the grain side
downwards on a table, and crated 3
with a mixture of oil obtained from sea
calves 4, and
that distilled from birch bark; the proportions are varied according to
circumstances, but for the most part, one of birch oil to two parts of the
other is the standard composition. This in quantity of about nine ounces to
each medium-sized skin, is laid on with the hand so carefully as to insure an
even and entire coat. This done, the skins are stretched upon cords in an open
shed, and left till dried.
The Baskirs and Kirguises 5 prepare their skins by smoking them,
in lieu of tanning. The hair is detached by scraping them, while in the green
state, with a broken sickle attached to a handle. When this is done, the skins
are attached to cords placed parallel to one another in a pit, the depth and
breadth of which depends on the number of skins to be treated at once, and
which is connected with another, at the distance of five feet, by a tunnel at
the bottom. The pit containing the skins is well covered, and a fire of dry and
decayed wood lighted in the other, which is likewise protected. As no immediate
means of escape exists, the smoke passes over into the pit charged with the
skins, by the tunnel or gutter at the bottom, and in the course of two or three
weeks that they are exposed to its action, converts them into a leather which
is said to possess a degree of impermeability superior to that of any tanned
leather.
The method pursued in
The skins are deprived of hair by steeping in a lime vat,
or in one containing a mixture of lime and potassa lie, but too weak to act upon the
fibre, and scraping on the beam 6;
they are then rinsed and fulled 7
for a longer or shorter period, according to their body, and subsequently
allowed to ferment in a steep, being first well washed in hot water. Eight days
are allowed for this operation, at the end of which time they are taken out,
again fulled and washed, and, if necessary, submitted a second time to the vat,
in order to open all the pores. When this is properly done, they are taken out,
well washed, placed on the beam, and worked with the flesher on both sides. After
this a paste is made, sufficient for two hundred skins, of thirty-eight pounds
of rye-flour. This is allowed to ferment, then diluted with a sufficient volume
of water, and the skins are immersed in it during forty-eight hours; and at the
end of this time they are transferred to smaller vats, and allowed to remain in
them for fifteen days, when they are taken out and well washed in running
water.
They are now fit for the tanning, which is done by putting
them into vats filled with extract of willow bark—salix cinerea and salix
caprea—of such a degree of heat as will not injure the animal fibre. Whilst
in this solution—usually a week—the skins are handled twice daily, and pressed
for half an hour each time; after this the decoction is renewed, and the same
course followed as when in the first bath, the time in the second case being
likewise a week. After this the skins are taken out and dried in the ordinary
way, when they are fit for currying with the empyreumatic 8 oil which gives this kind of leather
the virtues so much desired. In the execution of this part of the work, the
ordinary course is followed, fish oil being used first, with the requisite
shavings, stretchings, and pommelings, to render it pliable. The leather is then
grained by passing it between rollers weighted to the proper degree by levers
or some analogous means, and having on their surfaces raised threads parallel
to, and intersecting one another, to give the intended grain. After this the
skins are dried to the proper degree, and then oil of the birch, or Russian oil, is spread over on the flesh
side. The color peculiar to this kind of leather is then laid on, and in this
state the skins are repeatedly exposed to the rays of the sun, in order to make
the color penetrate into the pores; they are then well pommeled and slicked
with the lunette or circular knife on
the beam, and finally worked with a hard brush on the hair side. The red color
of Russian leather is produced with alum and a decoction of
In impregnating with the oil, great care is necessary to
have the absorption equal; at the same time, too much oil must not be employed,
lest it might pass through and stain the grain side. This is especially to be
guarded against when operating on small delicate skins; when it is desired to
confer some of the properties of Russian leather upon undyed, or
The method of manufacturing the oil of birch in
It appears from the experiments of Chevreuil, Payen,
and Chevalier, that the principle
to which the above oil owes its odor and other qualities, is a white
pulverulent substance 11 soluble in alcohol, which they call betulin;
it is volatilized by heat, and condenses into crystalline needles; thrown upon
live coals, it gives off thick white vapors similar to those emitted by Russia
leather under similar circumstances, but more agreeable.
Hungarian Leather.—By the method long known and
practised in Hungary, and latterly in France and other countries, leather is
prepared in a rapid way, and without the aid of tannin—mineral salts being substituted together with other
agents. The substance most generally resorted to for combining with and
preserving the tissue of the skin, in other words, for converting the latter
into leather, is sub-chloride
of aluminium, produced by the decomposition of ordinary alum by common salt. This
preserves the skin; and another kind of tanning process, with oil or tallow,
gives the leather suppleness, and prevents it from forming a hard body. In this
manufacture, the influence of the season, air, or other agents which affect the
labours of the ordinary tanner are not felt, in consequence of the brief time
it occupies, and the nature of the process. The requirements for carrying on
the business are fewer and more simple than those of the ordinary tanner. They
consist of a shed erected on the banks of a stream, wherein the beams for
paring, fleshing and unhairing are arranged, and the knives, scraping stones,
and other tools kept. A boiler and furnace for preparing the alum liquor is
fitted up in one corner, besides which are two larger tubs for immersing the
skins, together with a number of smaller ones. The other division of the
factory, where the oiling is done, consists of a room six and a half feet high,
by sixteen and a half square, capable of being
rendered perfectly tight 12. One corner of this chamber is occupied with the furnace
over which is placed a copper pan capable of containing one hundred and eighty
pounds of tallow; the sides are occupied by tables, whereon the skins are
greased; and the centre has a stone slab three feet and a quarter square, and
on this an iron grating is fixed, whereon charcoal is burned for the purpose of
flaming or heating the hides, as will be mentioned afterwards. The upper part
is furnished with poles for hanging the skins on.
In
tanning or preparing Hungarian leather, the principle preliminary processes are
analogous to those already described, only that instead of liming for the
depilation, the hair is carefully shaved off—that is to say, the skins are well
washed, cut in halves, shaved, and steeped for twenty-four hours in the running
stream.
The
greatest care must be exercised, and the most expert workmen employed for the
fleshing, paring, and shaving off of the hair, lest the skin should be injured,
and at best the operation is tedious, so much so, that one man can work no more
than a dozen or fifteen skins in a day. The shaving and washing being
completed, the hides are passed through the first alum bath, composed of six to
seven pounds of alum, and three and a quarter to four and a half pounds of
common salt dissolved in eight gallons of water, for every hide of seventy-five
to eighty-five pounds in weight. After raising the temperature of this solution
to about 120°, or a little higher, the hides or sides are arranged in parcels
of three or four in each, and deposited in two large tubs already mentioned,
the hair side being uppermost.
As much
of the liquor as will cover them is now poured in, and a workman stamps or
treads them out, passing backwards and forwards till the piece exposed to this
treatment is sufficiently worked, after which it is rolled up, and the same
operation proceeded with till every one of the parcel has received the proper
treading. After this, the partly-spent alum liquor is returned to the boiler;
and as soon as its temperature is raised, another quantity is ladled into the
vat, and the pieces of skin trampled out as above. A third and fourth treading
is given, using warm liquor each time, after which they are folded up and
deposited in a series of small tubs, about two feet high and eight inches in diameter,
and the spent alum menstruum poured over them. They remain in these tubs for
eight days, or longer in winter, being handled every day, and the liquor
freshened. At the end of this time the strips of skin are taken out and shaken,
or stretched, to remove creases, and the treated a second time exactly as in
the first aluming, save that they are left only twenty-four hours in the small
tubs, in contact with the saline water. After taking them out, they are laid
one upon another on an inclined plane, in order that as much of the alum liquor
as possible may run back into the vat. When thoroughly drained, the ends are
pierced at the corners, and wooden rods or laths thrust through; then one of
these is laid on cross-beams, and the piece of hide distended permitted to be
freely suspended. Here they remain for eighteen hours, and then they are taken
down, laid on the floor, and the workman, by folding and stretching, removes
the wrinkles and creases; this done, they are laid one upon another, and left
so for two days, then hung up by the laths on the cross beams till thoroughly
exsiccated 13.
The dried skins, before they are fit to receive the
oil, must be softened by treading them upon an inclined plane, suspended, as
shown in the figure annexed, by upright
and cross pieces firmly bound together. The strip of skin is laid doubled on
this plane, and a smooth stick placed in the fold, and the workman, laying hold
of the cross handrail, tramps upon the skin, and, by a shuffling motion of his
feet and body, causes every part of it to be pressed and smoothened by the
roller. To render the process more effectual, he wears thick-soled shoes. He
continues the work of tramping and shuffling the stick about in the fold of the
skin, till the latter becomes as soft and pliant as it is possible to make it.
Each strip or piece is thus worked, and subsequently exposed for a short time,
to be dried if necessary. After this desiccation, they are again slightly
trodden in the same manner as before, to erase any contractions and wrinkles, et cetera.
They are
now fit to be greased, and, therefore, are submitted to this operation. The
boiler, which occupies one corner of the air-tight chamber wherein this work is
done, is three-fourths filled with tallow, fish oil, or whatever else is used
for saturating the skins, and the whole heated by a fire outside the walls of
the apartment. When the temperature stands a little above the melting point, a
short-handled mop or dauber is dipped into it, and the fat spread equally in
this heated state over the flesh side, after which the strip is turned, and the
hair side brushed over with what remains in the dauber. Those which are first
greased are laid upon one another, flesh side upwards, successively, till the
entire number have been treated. They are allowed to remain for a time, to
enable them to absorb the fat as much as possible before flaming them. For this purpose, a fire of charcoal is lighted on a
grate, constructed on bricks in the centre of the room, and whilst it is being
lighted, the workmen, two in number, leave, closing the door tightly after
them. As soon as the charcoal is thought
to be incandescent, they open the door to allow the carbonic acid to escape,
and then enter, and taking the top strip of the pile, each by one end, expose
it, flesh side downwards, to the glowing fire, holding it at some distance, and
at the same time stretch it in all directions. The first so treated is laid on
and adjoining table, and the others as they have passed through the same
operation are piled upon it, the whole being covered with cloth as a protection
against cold draughts and the unequal effects of the fire. This treatment aids
in the absorption of the oil, and the stretching given at the same time
improves the product. After an interval of an hour, the hides or sides are
deprived of the excess of fat by wiping them. They are then thrown across poles
to dry, flesh side outwards. The last exposure gives them a consistency, owing
to the combination of the fat with the tissue and the saline matter united to
it. The direct rays of the sun and an increased heat are to be avoided in this
final airing, as neither is conducive to the improvement of the article. After
this airing the sides are weighed, stamped, or marked, and put up for the
market.
Hungarian
leather prepared in this way, without the intervention of acids or alkalies,
fermentation, or other matters and processes that are known to be more or less
injurious when making leather with tan, preserves all the tenacity and body of
the skin, combined with strength and great suppleness; for which, and for its
tractive power 14, it is much used by saddlers and harness-makers.
Tawed Leather 15.—In the preparation of this kind of leather, the conserving
agent resorted to is a subsalt of alumina, just as in the manufacture of
Hungarian leather. The skins most generally treated are those of sheep, lambs,
and kids, together with a few other light varieties. Generally, the
preliminaries required are performed in the ordinary way, only the skins being
more tender, demand greater vigilance to preserve them from injury. They are
well soaked in running water for the purpose of cleansing. If dry, as in many
cases, this steeping must be assisted by working of breaking them upon the beam with the back of the fleshing knife on
the inner side. After another rinsing, the skins are smeared with cream of
lime, or a mixture of lime and orpiment, gas lime, et cetera, on the flesh side, and then laid together in pairs, the
hair side being outwards. According to the efficacy of the depilating agent
employed, the time of the slacking of the skins extends from twenty-four hours
to several days. However, as soon as it is found that the hair yields, it is
separated, not in the usual way, but by plucking it out by sharp pincers. This
being done, the skins are smoothened by a roller of some such means; the
re-immersed for a short time in a weak lime-vat, from which they are removed to
another steep, and left to soak therein for ten to fifteen days, with
occasional handlings and examinations. When taken from the last vat, they are
ready to be submitted to the bran vat or ferment, similar to those already
mentioned, the proportions being forty pounds of bran in twenty gallons of
water. In this mixture the skins remain for a period of a fortnight or three
weeks in winter, according to the lowness of the temperature; but in summer,
when the weather is hot, two or three days suffice to raise them sufficiently.
In any
case, as soon as the skins sink in the menstruum—an occurrence which may be
hastened by stirring them frequently—the action of the steep is known to be
completed, and the skins are taken out and submitted to the first alum or white bath. This is composed of a
mixture of thirteen to twenty pounds of alum, and three to four pounds of
chloride of soda dissolved in boiling water, the solution being afterwards
diluted so as to saturate one hundred sheep skins. In summer the proportion of
salt is increased, in order to preserve the skins from any injury of a
putrefactive nature. The working of the skins is done in parcels, as in the
preparation of Hungarian leather, each parcel being passed successively through
the bath; after which, the whole are immersed for ten minutes. In some
tanneries, instead of simply steeping the skins in the latter bath, the alum
liquor is introduced at the proper degree of warmth, together with the skins,
into a cylindrical vessel with means for revolving attached, and worked for the
necessary time. The intimate contact of the skins with the whole of the liquid
in this case promotes, it is said, the combination of the basic aluminous salt
with the tissue, much more completely than is done in the other mode. The skins
intended to remain white are then put into a paste, made by adding to the alum
bath from fifteen to twenty pounds of wheaten flour, with gradual stirring, and
the yolks of fifty eggs well blended by brisk stirring. The skins are passed
singly through this menstruum, which is about the consistence of honey, and
afterwards the whole hundred are immersed, and allowed to remain in it during
the night. After this they are taken out, and suspended on poles to dry, and
left exposed for this purpose from eight to fifteen days, according to the
weather, being occasionally stretched both ways. When sufficiently dry, they
are worked upon the softening iron,
by which process any unevennesses are removed, the whiteness is developed, and
the whole uniformly stretched. They are next fixed on hooks, where the
stretching goes on—more, however, in the breadth than in the length of the
skin—being worked during the period of their thorough desiccation with the
stretching iron. In some cases the dried skins are submitted to a polishing
process, by rubbing them with pumice and giving the final gloss with a smooth
flat-iron.
These
operations suffice for the preparation of tawed leather, in which the alum salt
serves as tan, and the albuminous matter impregnated with it in the farinaceous
bath supplies the place of oil or fat in giving greater suppleness and
impermeability to the preparation than it otherwise would possess. Skins are
frequently tanned by this process, with the hair retained and dyed. All the
operations necessary in this case are the same as have been just detailed, with
the exception of those that aim at the removal or softening of the hair, which
are carefully guarded against. When dyed rugs are prepared, the wool is
colored, previous to the commencement of the tawing, by any of the ordinary
methods.
Tawed
leather is occasionally colored. The tinctorial matter, whatever it may be, is
laid on the grain side in a moistened state and while the skin is yet damp, and
worked into it by means of a stretcher, after which treatment the polishing and
smoothing take place.
Oil or Chamois Leather.—This article takes its name from the skins of the chamois; but , although the
term is still retained, those of sheep, deer, lambs, and the thin portion of
split hides and skins, are now converted into it. It is different from any of
the varieties hitherto described, because neither tannin nor mineral matters
enter into its formation; the conservation being entirely effected by means of oils
and fats. Further, the finest, as well as the coarsest quality known as wash-leather, receive precisely the same
treatment, and consequently the difference they represent is owing to the
circumstance, that the finest skins are chosen for the former, whilst the
inferior ones are made into the latter. In the last 16, sixteenth and earlier centuries, the
trade in chamois leather was much more considerable than at present; because,
in those periods, it was extensively used for clothing, particularly in the
armies 17.
It is now, however, abandoned for this purpose, in consequence of its
permeability, owing to which it readily absorbed moisture, and parted with it
but slowly; qualities which kept the wearer in continual danger of cold and
rheumatic complaints.
In the manufacture of chamois leather the skins are
prepared by passing through the lime vats, scraping on the horse, et cetera, in the ordinary way; and when
these preliminaries are effected, and the lime removed in the lactic acid or
bran vat, as much as possible, they are subjected to the frizing operation. This consists in rubbing them with pumice-stone,
or the blunt end of a round knife, till the grain is entirely removed, the
surface softened, and an equal thickness obtained throughout. After this the
skins are squeezed or pressed, in order to remove as much water as possible.
With this view they are placed in the trough of a fulling mill, such as is
represented in Fig. 353, after the large excess of water has been expressed,
and are there subjected to the action of the wooden hammers till they become
nearly dry. When this happens, they are spread out on the table to receive the
first charge of oil. That employed is usually cod oil, although any kind of
animal oil is made to answer. When this has been sprinkled upon them, they are
rolled up in bundles of four each, and then submitted to the action of the mill
for a period varying from two to four hours, or until the oil has united or
become absorbed in the pores of the skins. They are then taken out, unfolded,
and exposed to dry for a short time; then a second oiling is given, followed by
a fulling. It is necessary to repeat these operations several times, to insure
the proper saturation of the skin fibre. However long the action of the fulling
mill is continued, it is necessary to bring the aid of heat into requisition
before the combination of the fatty matter with the skin is completed. Heat is
applied generally by suspending the skins in a close chamber, furnished with
steam pipes, or warmed with a stove to the proper degree. It is supposed that
during this heating a fermentative change takes place, by which certain
deleterious matters are destroyed, and the skin is afterwards better able to
resist putrefaction, in addition to the more complete saturation of every part.
The
greater dilution of the oil by the increased temperature of the stove-room
causes part of it to exude on the surface, and this must be removed by
immersing the skins in a wash or bath, made with soda or potassa in water, and
of such density as will not dissolve the fibrous tissue. The skips 18 are steeped for an hour, and handled
in this bath, after which they are wrung at the peg and dried. To give the
finish, the leather is worked with the stretcher on the table, then on the
horse, and lastly, passed between rollers to give it the polish. The buff-color
which generally, though not always, distinguishes chamois leather, is given by
immersing the oiled skins in an infusion of oak bark, and afterwards wringing,
drying, et cetera. The tannin reacts
here as a dye, and not as a tanning agent.
For
supplanting the hand labour in frizing
and other operations, Nisbet has
patented machinery by which rough bodies and knives, mounted on revolving
cylinders, are made to rub against the skin. By this means a regularity in the
thickness and texture of the skin is obtained, which could hardly be obtained
by hand unless more than ordinary attention were bestowed upon the work, while
the time is curtailed to one-tenth of that required by the old method.
Morocco Leather.—Maroquin,
French; Saffian, German.—Before the
eighteenth century all morocco leather was imported from the Levant; but of the
way in which it was prepared, nothing was publicly known till the account of Granger appeared in 1735. About the middle of the last
century a manufactory was established at Paris, the first of its kind, in the
Faubourg St. Antoine; this in a few years was followed by another; and from the
impetus given by an increased demand, the trade continued to extend until, at
the present time, there are several manufacturers of this article to be found
in the different countries of Europe, and in the United States of America.
The skins
usually come into the tannery in the dried state; and the operations required
to render them as soft an pliable as fresh ones, and likewise to deprive them
of epidermis, hair, and particles of flesh, are so similar to those already
described in connection with the ordinary tanning processes, that a very brief
account of the method of treatment will be sufficient. The dried skins are
first immersed in water till they are sufficiently softened, and after this in
a fermentable bath of a weak nature, such has been used for a previous
operation. Here the softening is considerably assisted; but it is necessary to
watch its effects with much attention, lest it might be productive of injury to
the skins. When it is thought they have acquired the proper degree of pliancy,
they are worked on the flesh side with the disc or circular knife, to separate
the fatty and fleshy matters, and likewise to remove the creases produced in
the drying. This done, they are next submitted to the depilating agents, which
consist of a number of solutions of lime, increasing in strength from the first
to the last. Scarcely any difference exists between this part of the process and
that which is followed in tanning upper-leather; but as the retention of lime
or fatty matters is still more objectionable in skins intended for morocco,
owing to such matters being liable to produce spots or stains in the color
applied at a future stage, greater attention and labor are required for their
complete removal; hence after the unhairing, the fleshing, and paring of the
head and leg parts, and the short steeping in lime-water which is usually given
after this, the trimmed skins are introduced into a wooden cylinder moving upon
an axis, and having internally a number of wooden pegs rounded at the end. This
fulling machine is half filled with clean water, and, being charged with as
many skins as it will conveniently hold, it is set in motion. By the action of
the pegs and the movement of the skins and liquid, a considerable quantity of
the lime is separated, the water of the cylinder being frequently renewed. To
complete the depuration from lime, it is necessary to submit the skins to a
bath of fermented bran or flour disseminated in water, or to one formed of
dogs’, pigeons’, or pen-fowls’ excrements, and called as usual the bate or pure. After being in one or other of these, as the case may be,
from twelve to twenty-four hours, according to the strength and temperature,
they are taken out and scraped on the beam on both the flesh and grain side,
and examined for the purpose of rejecting those which are inferior or in any
way damaged. In some instances, instead of the bran vat or bate, a solution of honey or a decoction of figs has been employed,
together with a little salt, to steep the limed and unhaired skins in, on the
principle of Turnbull’s
patent, when the saccharine matter enters into a readily-soluble combination
with the lime, and washes out with facility. In either case the more perfect
skins which are set aside for the better quality of morocco, are prepared for
the operation of dyeing, which with them generally takes place before the
tanning, whilst the second and third qualities are colored after the tanning is
executed.
Red
and the bags thus formed are deposited in a large tun,
likewise containing a solution of sumac tan, as represented in Fig, 354, where
they are floated and moved about, so as to expose every part of the skin to the
action of the tanning agent. When the solution and tan in the leather bags are
supposed to be exhausted, the bags are taken out and laid on the rack adjoining
the tun, where they drain for some time; they are again filled with the strong
solution, floated and moved about in the large tub as before, till the tannin
has entered into combination. They are now removed from the tun, placed to
drain, till the contained liquor is emptied into the tun, ripped and cleaned
from the debris and impurities of the tanning material by thorough washing with
cold water. Any wrinkles are removed by working on the beam before exposing
them to the drying loft. During the desiccation, the skins shrivel so much as
to necessitate their immersion in water for some time, or the fulling of them
in a machine such as is used for making chamois leather, tepid water being
used. After fulling, several workings on the beam are given, as well on the
hair as on the flesh side, in order to remove the excess of sumac. One of these
workings consists of beating the tanned skin upon a table studded with
round-headed pegs, with the view of breaking up the small fibres, which
otherwise, by their contraction or expansion, would cause the articles made of
this kind of leather to become deformed. They are placed one upon another,
flesh side inwards, and stitched round, or indented with a blunt knife round
the border, so as to keep them temporarily together, whilst they are being
handled in the color-vat, and to prevent the dye being deposited on any other
part than the grain side. For all shades of color, with the exception of blue
and black, a steep of Campeachy wood is employed, heated as hot as the hand can
bear; this is put into a rectangular vessel, and the two skins laid into it
carefully, and pressed and worked, so as to induce the penetration of the
liquor, but not to remove them from one another. Several immersions are
required with fresh coloring matter, till the proper tint is obtained. Much
practice and attention are necessary to immerse and work the skins in the
dye-vat, in order to stain them efficiently, and prevent the color running on
both sides.
Black
morocco is prepared by applying with a brush, on the grain side, a solution of
sesquiacetate of iron. The azure tint is given by means of the cold indigo-vat,
or with Prussian blue; violets and purples are produced by giving two coats of
blue, and afterwards passing the skins through a bath of cochineal, the
strength of which is regulated according to the shade required; yellows are
obtained by working with quercitron 21
root, finely ground and digested to abstract the color; this dye is very
brilliant and stable. By modifying the work and multiplying the immersion
baths, any shade intermediate between those described can be obtained.
The dyed
skins are now placed on the plate of the hydraulic press, and the excess of
dye-stuff expressed, after which they are worked on the beam, to remove creases
and wrinkles, and dried; first spontaneously in a current of cold air, and
afterwards in a heated atmosphere. Before being perfectly dry, however, they
are worked with the knife, slicker, and pommel, as in the operation of
currying, whereby they acquire suppleness and equality of substance throughout.
They are then well polished, and the peculiar grain of morocco leather given. The
latter is done sometimes by hand, but more generally by machinery.
Rollers,
having raised parallel straight or diagonal threads, give the indented or
wrinkled appearance, which distinguishes this kind of leather. When the skins
are merely tanned, as when intended for the shoemaker, and then curried, the
operations of the last process are such as are applied to delicate calf skins,
only that as the goat skins are so much thinner, much greater care and delicacy
of manipulation must be exercised in all cases.
Skiver and Roan.—Skiver is
a leather prepared from sheep skin and sumac, like imitation morocco, only the
skins are split by machinery. In tanning the sections, however, the practice
differs from that followed when preparing the morocco leather, inasmuch as the
sewing of the skins into bags is omitted, the extreme thinness of that intended
for skiver adapting it to combine with the tan more readily when spread out in
the ooze. Roan is sheep skin tanned
like morocco leather in all its details, but wanting the grain given to the
latter by the grooved rollers in the finishing processes.
Before
closing this article, it may be proper to give a short notice of two other
materials, which, though not leather in the proper sense of the term, are
nevertheless analogous to it; these are Parchment and Shagreen. Both are
prepared from the same kinds of skin, but generally the stronger and coarser
kinds are reserved for the latter.
Parchment.—This article, undoubtedly
of Eastern origin, is said to be the invention of Eumenes, king of Pergamus 22, in Asiatic Turkey, who reigned about
200 years before Christ. It was
much used as a substitute for the papyrus,
owing to its durability; and even at the present time it is the article in
general use for valuable writings, such as deeds, wills, and the like. The fine
parchment used for such purposes is manufactured from the skins of young
calves, kids, still-born lambs, sheep, and goats; but when intended for coarser
purposes, such as drum-heads
and the like, those of older calves, wolves, asses, and he-goats, are taken. Soaking or fulling, liming till the hair is
softened, scraping, fleshing, and washing, prepare the skins for the process of
conversion into parchment, properly so called. It consists firstly in
stretching the cleaned pelt upon a circular hoop, or more generally upon a
rectangular frame, furnished with holes, pins, and screws, or skewers and
cords, for exerting and required tension. This machine is usually fixed against
the wall of the building, for the purpose of facilitating the scraping and
rubbing of the drawn skin, after it has been sufficiently extended by the pins
and skewers. The preliminary scraping effected with a double-edged semicircular
knife, formerly referred to, removes adhering flesh and other extraneous
matter. After the fleshing, the frame is turned, and the grain side carefully
rubbed with the blunt edge of the knife, to throw off the exudations of dirt
and moisture. Then follows the grinding,
which consists in sprinkling the flesh side with finely-powdered chalk, or
slaked lime, and rubbing with a piece of pumice-stone, the face of which is
previously flattened upon a sandstone. By this operation, a further portion of
the assimilated moisture is taken up. A slight rubbing with the pumice-stone is
then given on the grain, but no lime is used, and afterwards the drying is
allowed to go on gradually out of the sun’s rays. In cold weather, the freezing
of the moisture in the skin would be injurious; and is, therefore, carefully
guarded against by keeping the temperature of the room above 32°, or by
protecting the skins with cloths. Towards the completion of the desiccation,
the skewers are further tightened. Finally the white appearance given by the
lime is removed by careful rubbing with the woolly side of a lamb skin. Should
grease stains be now detected, it is necessary to immerse the skin anew in a
lime-pit for eight or ten days, to remove them; this induces the formation of a
lime soap with the fatty matter, and consequently the deletion of the spots. The
pelt is again stretched on the horse
or frame, and dried, and then transferred to the scraper, who mounts it upon a frame like the last, the tail end
downwards, and stretches it with the cords only, on a support of well-extended
crude calf-skin. Here it is carefully pared with a larger and sharper knife,
but similar to the one used for fleshing,
to remove inequalities, and then scraped on the grain or outside, till a
perfectly even, smooth surface is given. Whatever is wanting in this operation,
is remedied by a further rubbing with a very fine-faced piece of pumice-stone
on a cushioned support. Any defects in the skin, such as holes and the like,
are removed by carefully paring round the edges of the injured part, and
tastefully patching suitable pieces on with gum-water.
The green
color of parchment is given by spreading with a brush a solution, made with
thirty parts of crystallised acetate of copper and eight of bitartrate of
potassa in five hundred of rain or distilled water, four parts of nitric acid
being added to the mixture when cold. It is necessary to moisten the skin
before applying this dye. Finally, the lustre is given by rubbing the surface
with a solution of albumen or gum
arabic.
Shagreen.—The article known under
this title is very analogous in its nature to parchment, and consequently is
not a true leather. Like parchment, it was originally an Eastern preparation,
and is still principally obtained from Astracan
and Asiatic Russia. From the accounts obtained for the manufacture, it appears
that only the hides of horses, asses, and camels, are appropriated to its
production, and of these only the small strip from the crupper along the chine
to the neck is used.
The
strips cut out of the proper size, are steeped in water till the hair softens
and gives readily, when it is removed by scraping; they are again steeped and
worked by the flesher, till all the matter extraneous to the skin is separated,
and the skin itself is reduced to the proper thinness. They are now mounted on
the herse, or
horse, and stretched thoroughly, being occasionally moistened to favour the
stretching.
As soon
as this has been carried sufficiently far, the strips of skin are placed on the
floor and covered on the grain side with the seeds of the alabuta or goosefoot—chenopodium
album. A covering of felt is then laid on, and the seeds are pressed
into the skin by trampling on them, or by the use of mechanical pressure. The
skins, still bound in the frames, are then dried, till the seeds begin to drop,
when the latter are shaken off. At this stage the skins appear dry, horny, and
deeply indented. They are next placed on a padded horse, and shaved till the
indentations caused by the seeds become very shallow and of uniform depth,
after which they are steeped in water and the in a hot alkaline lye, and piled
one upon another whilst in a hot moist state. During the time they are so left,
the compressed parts swell out, forming as it were embossed balls on the skin,
and thus constitute the peculiar appearance of this preparation. Shagreen is
dyed of various colors; red is obtained with a decoction of cochineal, in the
same way as morocco; blue by the cold indigo vat; black, by steeping the skin,
or brushing on the side intended for the dye, a solution of tannin, and
afterwards one of sulphate of iron—copperas; and green, by moistening with a
dense solution of chloride of ammonium—sal ammoniac—and sprinkling the part so
moistened with copper turnings and rolling up the strip, keeping the grain side
inwards. The ammoniacal salt dissolves a portion of the metal and forms a
subsalt with it, which enters into combination with the skin, and gives a
bright hue. To finish the article, the dyed strips are carefully greased and
worked in hot water, then rubbed with blunt tools and dried.
Shagreen
of an inferior quality has been made from sheep, goat, horse and even fish
skins; the treatment they receive is analogous to that already described, but
fir the most part, where the skin is weak, a slight tanning is allowed before
shaving, and the skin is stretched more in the direction of its length rather
than cross-wise. The grain is given by pressing the prepared skin on warm
copper plates, engraved so as to imitate the appearance of the genuine
shagreen.
In preparing this account of the leather
manufacture, much of the information, besides what has been derived from
private sources, has been obtained from Doctor Morfit’s 23
able work on Tanning, Knapp’s
Technology, Schubart, Dumas, Parnell,
Sullivan, the Catalogue of the Irish
Industrial Exhibition, and other authorities.
Statistics.—The following table expresses the imported
quantities of the principal tanning materials in 1849 in hundredweights:—
|
|
Tanning Bark, et cetera. |
Terra Japonica. |
Sumach. |
Valonia |
|
|
141,392 |
— |
140 |
— |
|
|
114,180 |
— |
— |
— |
|
East Indian empire, |
— |
169,140 |
— |
— |
|
|
1,166 |
— |
218,380 |
— |
|
|
— |
— |
— |
296,000 |
|
|
42,318 |
— |
— |
— |
|
Australian territories, |
— |
— |
29,840 |
15,820 |
|
|
27,619 |
— |
— |
— |
|
|
12,784 |
— |
— |
— |
|
|
9,594 |
— |
440 |
— |
|
|
9,931 |
— |
20 |
4,320 |
|
|
4,563 |
— |
— |
— |
|
|
— |
— |
— |
4,280 |
|
|
— |
— |
— |
10,480 |
|
Miscellaneous, |
5,035 |
— |
2,980 |
2,520 |
|
|
______ |
______ |
______ |
______ |
|
Total, |
368,582 |
169,140 |
251,800 |
333,420 |
Footnotes
1. ^ A solvent, a liquid by which a solid may be
dissolved. The use of this word derives from Alchemy. There, the base metal
intended for transmutation was likened to the seed within the womb in relation to
the blood of a woman’s monthly or menstrual, blood flow. Menstruum is the neuter nominative form of the Latin adjective, menstruus, monthly (OED). Here the meaning seems to have
slipped to ‘a mixture, part dissolved and part dispersed in water’.
2. ^ Softened by steeping in a liquid (OED maceration, n. 2).
3. ^ Sic.
Quite what it means is not clear. A crate is a hurdle or a
large wickerwork hamper (OED
crate, n. I & 2).
4. ^ Sea
calf: the seal, especially the common seal, Phoca
virtulina (OED calf, 4).
5. ^ I imagine these will be the peoples of Bashkortostan, in the
southern Urals and Kyrgyzstan,
on the western Chinese border, respectively. The two states are separated by
6. ^ The beam is shown in Fig. 347.
7. ^ This is treading or beating (typically cloth
but here, hides) for the purpose of cleansing and thickening (OED). A description of cloth fulling is linked here.
8. ^ Tasting or smelling of burnt organic matter (OED empyreumatic, a.). (The Empyreus is the fiery Heaven
or sphere of fire.)
9. ^ Iron(II)
sulphate.
10. ^ Repeated distillation: compare rectified spirit.
11. ^ powder or dust (OED pulverulent, adj. 1).
12. ^ Air tight: hermetically sealed.
15. ^ To taw is to prepare or dress some raw
material ready for a further process. It may be hemp or as here, hides. The
term is used more specifically for the preparation of Hungarian leather (OED taw, v.1
2).
17. ^ There, the leather was heavier than the
typical wash-leather and was known as buff. It gave its name to the East Kent
Regiment, The Buffs and the Yellowbelly name for
18. ^ Skips is the word which Muspratt
uses, here but nowhere else in the leather article. However, in 1688, goat
skins were reckoned by the skip, which was fifty skins
(OED skip, n.5).
19. ^ The German name of the city of Klaipėda,
now in
20. ^ Essaouira,
on the coast of Morocco
21. ^ This
name comes from the botanical name of oak, quercus
and from the lemon colour, citron, which it produces. Quercitron
is a shortening of querci-citron. It is produced from the black oak,
Quercus tinctoria
and its active agent is known as quercitrin
(OED quercitron,
n.).
22. ^ This
is probably one of the kings of Pergamon.
23. ^ This is probably Campbell Morfit,
a noted chemist, born in Herculaneum,