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. Russia was long the only country that produced it, but it has lately been manufactured in Paris. Its odor and particular qualities are attributed to the essential oil of birch bark, with which it is impregnated after the tanning with this material. In Russia, it is manufactured from all kinds of skins, but in Paris, and wherever else the product is imitated, only sheep and goat skins are operated upon.

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 France for making Russian leather is as follows:—

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 Brazil and sandal wood, and the black with a solution of sulphate of iron—copperas 9—and sandal-wood

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 Morocco leathers, the quantity of birch oil necessary is very small.

The method of manufacturing the oil of birch in Russia is somewhat rude. The white membranous matter of the bark of the tree, deprived as much as possible of woody fibre, is introduced into an iron vessel of suitable dimensions till the latter is full, when the cover, of an exterior convex shape, is fixed on. From the middle of this lid an iron tube issues, and enters to about three-fourths of the depth of another iron receptacle placed over the former. The edges of both vessels are well bolted and screwed together, and the whole inverted, so that charged with the bark is uppermost, and the empty one beneath. In order to condense the oil as much as possible, the empty receptacle is buried in the ground to keep it cool; the top one is then secured by a coating of cement made of clay and sand, and when dry, surrounded with a wooden fire till it is raised to a red heat, which is continued till the distillation is completed. When the two vessels are detached, the upper one is found to contain a light friable charcoal, and that serving as a condenser, a brown oily empyreumatic liquid, possessing a very strong odor, some tar, and pyroligneous acid. The product, being depurated from tar and acid, is retained in well-close vessels for use of the currier. In France, the bark is distilled in copper vessels, and the heavy oil condensed in a tube passing through water, or an ordinary worm. About six per cent. of the bark passes over, but the oil, which is highly colored, is not very abundant; by rectification 10, however, it can be obtained almost colorless, in which state it is better adapted for oiling white leather than the original product, as it does not leave any stains.

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. Morocco is commonly known as a colored leather, having an indented or wrinkled fibrous appearance. The genuine or true variety is made from goat skins; but another kind, known as imitation morocco, is manufactured from sheep and lamb skins. As stated in the introduction, in connection with the subject of skins, the best kinds for this purpose comes from Switzerland; but the English manufacturer draws upon other countries for his supply, such as Germany, Memel 19, Mogadore 20, East Indies, Cape of Good Hope, and several others. Compared with sheep skins, those of the goat have a closeness of fibre, a body, and strength that render them much superior in point of appearance and durability. In France, the Spanish goat skins are highly esteemed, and, consequently, a good many are imported from that country.

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 Morocco.—The perfect skins are placed together two by two, so that the parts of one correspond with those of the other, the flesh side of each being inwards, and then sewed around the edges sufficiently close to retain the air which is afterwards blown into them so as to swell them into a kind of bag. In this state, on being plunged into the mordanting liquor, only the surface destined to be dyed takes up the substance or the mordant, and consequently of the dye afterwards, and therefore no waste is incurred. The mordants are generally alum, chloride of tin, wine-stone, or such substances; but the tin-salt gives the finest shade of color. The mordant liquor of either of these, sufficiently diluted and warm, is put into a suitable vat or vessel, and the swollen skins immersed for a few minutes in it, then withdrawn and allowed to drain where the drippings may flow back into the vat. Afterwards they are worked on the beam with the view of giving them a grain, and expelling the excess of liquor more completely. This treatment prepares them for the dye, which is usually cochineal, as it gives the brightest color of any. For each dozen of skins from twelve ounces, or less, to sixteen is taken, according to the size. It is finely powdered, and suspended in water to which cream of tartar or some alum has been added. The whole is then boiled for some time in a copper, filtered through a fine cloth, and divided into two equal portions to give two successive immersions. The skins sewed up thoroughly are placed in the tun with half of the dye liquor, and well agitated for about half an hour, after which time the liquor is replaced by the second portion, and the motion of the contents prolonged for a further half hour, when the dyeing will be completed. The skins are now taken out and submitted to the tanning operations, which are the same as will be presently described. Finally the sewing is ripped; the skins—now tanned leather—well rinsed in fresh water, worked on the beam to render them supple add remove creases, dried, pommeled, slickered, and grained in the ordinary way. Sometimes the dye is brightened by passing a sponge saturated with a solution of carmine in ammonia over it, after the partial drying that follows the tanning and rinsing, et cetera. Also the skins are wetted with a decoction of saffron, in order to obtain a shade of color approaching to scarlet.

Morocco of other shades of Color.—Morocco leather of other colors is tanned previous to fixing the dye upon it. After the depilation and bating, or branning, as the case may be, the pelts are placed in a revolving cylinder with the tanning agent, which is always sumac, and a proper quantity of water slightly heated, and the agitation kept up for some time, by means of connecting or driving bands, and drums on the axis of the cylinder, and on the main or other shaft of the engine. The first tanning is given with sumac, partly or half reduced, and suspended in water, so as to form a thickish paste, and finished by substituting a new bath of fresh sumac; the motion of the cylinder being maintained whilst the skins and tanning agent are in contact. With this method, the formation of leather is very rapid, requiring only twenty-four hours. The tanned skins are now removed from the cylinder, rinsed, so as to clean them from the sumac, and exposed in the drying-room; and when the assimilated water is removed, they may be stored or at once submitted to the process of dyeing, according to the requirements of the tanner. Another method is also much followed, as well with skins that have been dyed red as with those not so treated; it consists in employing a decoction, or ooze of sumac, and filling the skins with it, they being sewed two and two together for this purpose, having the flesh sides inwards, as already detailed. A quantity of powdered sumac is then introduced into each through the aperture, and afterwards a decoction of the tan; the opening is now secured, 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

Belgium,

141,392

140

Holland,

114,180

East Indian empire,

169,140

Naples and Sicily,

1,166

218,380

Turkey,

296,000

America,

42,318

Australian territories,

29,840

15,820

Morocco,

27,619

Norway,

12,784

Spain,

9,594

440

Tuscany,

9,931

20

4,320

Australia,

4,563

Syria,

4,280

Greece,

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 Kazakhstan. Their homelands around the year 1200 are shown in the linked map. See also, Bashkirs and Kyrgyz. The modern distribution of Kyrgyz ethnicity is shown in the linked map, in which the Bashkirs appear to be lumped in with Russians and others.

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.

13. ^  Dried.

14. ^ Tensile strength.

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).

16. ^ The eighteenth century.

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 Lincolnshire people is said to come from a similar source, by way of the Royal North Lincolnshire Militia. The same sort of leather was used for polishing, that is buffing, metal.

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 Lithuania but formerly at the northern end of the coast of East Prussia.

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, Missouri on November 19, 1820.


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