Animal Proteins Part 8

The skins are obtained from all quarters of the globe where goats exist, and the excellent quality of the leather produced has created a demand which is greater than the supply. This is due not only to the demand for morocco leather, but also to the popularity of the goatskin chrome upper leathers such as "glace kid" (see Part III., Section IV.). The large American trade in the latter has produced the saying that wherever there is a goat there is an American waiting for it to die! The European supply of skins is somewhat limited. They are obtained from the Balkans and Bavaria, in which case they are small, fine-grained and plump skins.

The Swiss goatskins are larger, and have also a fine grain; they are well grown and well flayed. Scandinavian skins have a poor reputation, being very flat. The African supply is important; Abyssinian skins are exceedingly compact and tough, and are very suitable for "bold grain"

finishes. The Cape skins are particularly large, strong and thick, but their quality is often impaired by the cure, the skins being flint-dry, and, like hides so cured, p.r.o.ne to unsoundness. Large quant.i.ties of goatskins also come from the East. Many of these are imported in a tanned state (E.I. Goat). These skins are tanned with turwar bark, which contains a catechol tannin. They are also heavily oiled with sesame oil, and need degreasing. The tannage is also stripped as far as practicable, and the skins retanned with sumach before finis.h.i.+ng. They make good morocco leathers for many purposes, but the primary catechol tannage renders them ineligible for finis.h.i.+ng under the specifications of the Committee of the Society of Arts. The skins have a Persian or Indian origin. India also supplies a large number of raw dried goatskins which are small and of variable quality. These, however, are more extensively used for chrome uppers.

Goatskins are imported in either a salted or a dried condition. The great aim of soaking is to obtain the skins in a thoroughly soft condition. Hence the soaking is prolonged, and some mechanical treatment is desirable in addition to various steepings in water. To be certain of softness it is desirable to avoid the use of alkalies in the soak waters, for although they cause hydration of the fibres by imbibition, they also have a plumping effect which is not wanted at this stage.

Salted goatskins are first immersed in water and left until the following day. This dissolves the salt. They are then stretched and given a fresh soak liquor of water only to soften further, clean, and remove the rest of the salt. This second water lasts only a few hours, and the goods are then drummed well in running water. This not only cleans quickly, but has an excellent softening effect. They are again returned to a soak liquor, then softened mechanically by working them over a beam. This treatment must be repeated, drumming again if necessary, until the skins are perfectly relaxed and thoroughly softened. If the treatment be very prolonged it becomes advisable to use antiseptics in the soak waters after the first drumming. Solubilized (or emulsified) cresols of the "Jeyes fluid" type are the most suitable antiseptics, but too much must not be used or the sterilization affects the liming, in which bacterial action is needed. Flint-dry skins are left longer in the first soak, which should be of water only. They are then given a fresh soak liquor containing 0.2 per cent. of sodium sulphide. Sometimes a 1.0 per cent. solution of borax is used instead; it softens excellently, is antiseptic, and avoids the plumping effect, but is rather expensive. The goods are next drummed well, and resoaked and worked as for salted skins. In either case the soaking takes about a week.

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

The sulphide of soda also commences the plumping action which follows in the next round, but this alternative has the disadvantage that the skins are unhaired whilst the pelt is swollen with sulphide, which renders the grain both harsh and tender and consequently more liable to damage by the unhairer's knife.

Deliming is by puering and drenching, and is often a.s.sociated with a further mechanical working of the goods. The skins are inserted into a puer liquor at 85 F. and thoroughly pulled down. The caustic alkalies should be completely neutralized. A slight cut into a thick part at the b.u.t.t end should develop no pink colour with phenolphthalein. The skins should be thoroughly relaxed, and the swelling so much eliminated that they are quite soft, weak and "fallen." The resilience and elasticity of the plumped skins should have quite disappeared, and the impressions of hand or thumb should be readily retained by the pelt. The grain should appear white and possess a soft and silky feel. In this condition they are again worked over the beam to soften further if possible. They are then rinsed and again worked over the beam. Drenching follows with 10 per cent. of bran on the pelt weight, the operation commencing at 85 to 95 F., and lasting till next morning. The skins are next scudded thoroughly to remove all dirt, but carefully so as not to damage the grain.

In tanning, sumach and oak bark are the staple materials. Sumach gives a much lighter colour, and hence it is used alone for goods that are to be dyed the lighter shades, but oak bark is a "faster" tannage and more preferable for dyeing in those cases where blacks and very dark shades are wanted. For ordinary purposes a blend is usually employed. A feature of oak bark, also, is that it tends to make a firmer leather, so that the proportion used must be adjusted with this fact in mind as well as the question of colour. For firmer moroccos the skins may pa.s.s through a handler round of oak-bark liquors (10-20) in which a certain amount of sumach is added to the liquors. The sumach is leached and a.s.sists both in tanning and bleaching as the liquor works through the round. The old liquor is run to a paddle, and the tannage is commenced by paddling the drenched skins in this liquor. It is advantageous both for the tannage and for the efficient "spending" of the sumach if this liquor be slightly warmed. In the early pit liquors the goods are very frequently handled. There is, however, the usual tendency of the times to save labour in this direction, and hence it is common to have several paddles with liquors of gradually increasing strength, followed by a shorter round of handlers in which the handling is more infrequent. Instead of paddles latticed drums may be inserted into pits containing liquors.

These, however, are not quite so convenient. In some tanneries, especially where sumach only is employed, the tannage is in paddles throughout. A new liquor is made up with fresh sumach and is used repeatedly until exhausted. A three-paddle system sometimes obtains, in which case the operation closely resembles the three-pit system of liming (Part I., Section II.), and the skins pa.s.s through an "old"

liquor, a "medium" liquor and a "fresh" liquor. The goods need not be paddled the whole day through, and indeed in the later stages this is undesirable. The packs remain several days in each liquor and take up to 14 days to tan. Two to three bags of sumach are needed for about 20 dozen goatskins. This method of tanning is efficient and convenient for bold-grain finishes, on account of the constant tumbling and bending of the skins which tends to work up a grain. For very soft leathers and fine-grain finishes, however, the "bag-tannage" or "bottle tannage" is favoured. In this method the pelt is st.i.tched up by machine to form a bag, grain outwards, leaving a "neck" in the hind shank. The bag is nearly filled with a fairly strong infusion of sumach, inflated with air and tied up at the neck. The bags are then placed into a vat of warm sumach liquor, in which they just float. The bags are pushed down and the liquor stirred up, so that the goods are in constant motion. After a few hours they are piled on a rack, and the tan liquor of the interior is caused to diffuse through the skins by the pressure due to the weight of the pile. The bags are refilled with fresh and stronger sumach liquor and the process is repeated. The skins are thus lightly but effectively tanned in about 24 hours, and the leather has very fine grain and soft feel. However tanned the skins are dried out after tanning, and sorted in the "crust" according to size and colour. The larger skins are preferred for upholstery and the smaller for fancy goods and bookbinding.

To ill.u.s.trate the course of finis.h.i.+ng operations, the case of hard-grain morocco for bookbinding may be given as typical. The goods are wet back with warm water and drummed for 1-2 hours in warm sumac to prepare for dyeing. They are then struck out by machine, sammed and shaved. Dyeing follows, with acid colours, in a drum. The goods are run first in a little water and the dyestuff added very gradually through a hollow axle. The acid required (preferably formic) is added later to develop the full shade. Warm solutions are used, and the dye bath is practically exhausted. The goods are next placed in cold water to wash off superfluous liquor and free the skins from acid. They are then horsed to drain, struck out and hung up to samm. They are seasoned with milk and water and piled to temper. They are "tooth rolled" in the glazing machine two ways: right-hand shank to left fore shank and _vice versa_, and piled again. After wetting back again they are "wet grained" by hand with a cork board in four directions: belly to belly, shank to shank, and across as before, and finally from neck to b.u.t.t. They are immediately hung up in a warm shed to dry, and to fix the grain. They are then softened by "breaking down" with a rubber board, top seasoned, piled to temper and dry, brushed lightly, piled again, brushed more heavily, and dried out. They are finally softened by graining in three directions: shank to shank and across, and neck to b.u.t.t. They are then brushed again. If these skins are wanted for upholstery they are shaved after dyeing, and nailed on boards to samm. They are also dried out in a cooler shed or "stove," to ensure softness.

REFERENCE.

Bennett, "Manufacture of Leather," pp. 39, 55, 89, 111, 204, 344, 396.

SECTION III.--SEALSKINS

A special cla.s.s of morocco leather is manufactured from the skins of seals. This should not be confused with the "sealskin" of popular parlance, which is manufactured from the skin of a different animal. All the fin-footed mammals (_Pinnipedia_), except the walrus, are termed seals, but they are divided into two families. The _Otariidae_ are known by their possession of small but distinct external ears: into this cla.s.s fall the fur-seals whose skin is dressed with the fur on, for women's jackets, m.u.f.fs and caps. The _Phocidae_ are that family without external ears: the skins of many species (_Phoce Greenlandica_, _Phoco barbata_, etc.) of this family are unhaired and given a vegetable tannage, thus forming the raw material of sealskin morocco leather. It is with the latter that this section will deal.

As the seal is a marine animal and is partial to the colder seas, its skin is very oily. The skins are imported in a salted condition from both the Arctic and Antarctic regions. North Europe, North America and Newfoundland supply many skins, and the southern material is supplied chiefly through the Cape. Sealskin shares with goatskin the properties of compact texture, strength of fibre, and great durability, all of which fit it for the manufacture of moroccos for upholstery, bookbinding, etc. It is, however, readily distinguishable from goatskin by its characteristic grain pattern.

In soaking sealskins the object is not only to soften thoroughly, but also to effect the recovery of as much seal oil as possible before the liming commences. This is desired because the oil is in itself a valuable bye-product, and because its removal is essential to a satisfactory liming and tannage. The removal of the oil is materially a.s.sisted by raising its temperature, so that the soaking of sealskins is often done with warm water (85-88 F.), after which treatment they are laid over the beam and sc.r.a.ped with a blunt knife on both flesh and grain. The oil flows away into a special receptacle. This treatment is repeated until the bulk of loose oil is removed. The process is known as "blubbering" or "brus.h.i.+ng over." After some soaking the skins are drummed to ensure softness. The skins are then fleshed. More oil may be obtained from the fles.h.i.+ngs.

By fles.h.i.+ng before liming a more regular action of the lime is obtained.

This is necessary to "kill" the grease still remaining in the skin. A long and mellow liming is given for the same reason. Fully three weeks are given, and old limes are much preferred, partly to obtain the maximum lipolytic action and partly to avoid the intense ribbing of the pelt which new limes so easily impart to the older animals. These ribs are very difficult to eliminate in the subsequent work. Some factories find it necessary to finish up in new limes, however, in order to plump and split the compact fibre bundles into their component fibrils. The plumped pelt is also easier to split green. No sulphides are usually employed. Sweating (see Section IV.) is sometimes used for depilation, and in this case the ribbing of the pelt does not take place.

The puering is unusually thorough with sealskins. This is to obtain the maximum softness and take full advantage of the lipolytic action. The puer liquor is fully 95 F., and the skins are paddled for about three hours, or until fully pulled down and completely delimed. Scudding follows, now usually by machine. The skins are then well drenched. The action is intensified by the use of peameal in addition to the bran.

About 10 per cent. of the mixture on the weight of pelt is used. It is customary, however, to drench at a lower temperature (68-70) than in the case of goatskins (Section II.), but the goods are left in the drench overnight only, as is usual in drenching. It is quite possible that drenches worked differently may have also a somewhat different fermentation and be due to other organisms than the symbiotic bacteria discovered by Wood. It is equally possible that the acids produced are also different, in relative proportion, if not in nature, and that consequently there is a real difference in the practical effect. In the Author's opinion, the great probability is that in the drench are several fermentations, and that if the action be reduced by lowering the temperature, but intensified by adding peameal to the bran, some of these fermentations are encouraged at the expense of others.

The tannage of sealskins depends upon the size of the skins, the purpose for which they are intended, and whether they have been split or not in the limed state. The largest and coa.r.s.est skins intended for boot uppers, and those which have been heavily scratched on the grain and are only suitable for enamels, are given a tannage which may last about 5 weeks. The liquors are made from oak bark and mimosa bark, and are made up to 35 with gambier and possibly myrabolans extract. For fancy work also heavy skins are used, but a softer tannage is needed. If for blacks the tannage is with gambier and chestnut extract. Two sets of handlers are given (10-15 and 15-20), using only gambier in the green sets.

They are well sumached after tanning to bleach and to mordant. If for colours, only sumach and oak bark are employed. The skins are first paddled for 3-4 days in sumach liquors, in which they are coloured through. The liquors may be warmed; this quickens the tannage and also leaches the sumach. The skins are then split, and the grains pa.s.s through a handler set with liquors made from oak bark (8-24). The skins are in this set for 3 weeks, in the first half of which they are very frequently handled. They are finished off by paddling for 1 or 2 days in a fresh liquor containing much sumach, which mordants the skins and bleaches the bark tannage. The flesh splits are given a drum tannage in chestnut and quebracho extracts. If small skins are being tanned for bookbinding purposes, sumach only is employed, and usually the tannage is entirely in paddles.

In finis.h.i.+ng many types of grain may be obtained, in blacks and in colours. The finis.h.i.+ng of "black levant" may, however, be selected as a typical case. The skins are soaked back, tempered, and either split or shaved, according to their substance and the size of grain wanted. The thin skins of course give the fine grains. Mixed tannages need scouring and possibly sumaching. The skins are then oiled up with linseed oil, sammed, set out and blacked. In this last operation the grain is brushed over with a solution of logwood and ammonia, and afterwards with the iron mordant which often contains glue. They are next hung up for a while and then "wet grained" in four directions--belly to belly, shank to shank, across, and neck to b.u.t.t. After hanging up in a hot stove to set the grain, they are cooled, fluffed on the flesh, and seasoned on the grain with a solution of milk and blood. A little black dyestuff may be added to the season. The season is well brushed in, the skins dried somewhat, and then glazed. They are then grained four ways again as above, dried out in the stove, and lightly oiled with warm linseed oil on the grain.

REFERENCE.

Bennett, "Manufacture of Leather," 40, 56, 90, 112, 206, 251, 312, 346, 383.

SECTION IV.--SHEEPSKINS

The most numerous cla.s.s of skins for light leathers is from the common sheep. These skins have particular value inasmuch as they include the wool as well as the pelt. This wool, which is actually the most valuable part of the sheep's skin, is the raw material of our woollen industries, and is one of the most important of animal proteids. We have, therefore, in this section to consider this dual value of sheepskins, the proteid of the epidermis (wool), and the proteid of the dermis (pelt); one the raw material of the woollen industry, the other the princ.i.p.al raw material of the light leather trade. The first problem is to separate the two proteids. With other skins and hides the ordinary liming processes were sufficient and appropriate, but in the case of sheepskins the method is unsuitable, because the exposure of the wool to the action of caustic lime and possibly other alkalies would seriously impair its quality and reduce its commercial value. Hence this separation of wool from pelt is usually quite a separate business, viz. that of the "fellmonger," whose occupation it is to collect the sheepskins from butchers and farmers, to separate the two important const.i.tuent proteids, and to hand the wool in one direction to the "wool stapler,"

who sorts it according to quality, and to hand the pelt in another direction to the light leather tanner, who tans and finishes the pelt to fit it for light upper work, fancy goods, etc.

In the first instance, therefore, we have to consider the work of the fellmonger, the separation of wool and pelt. In this work the wool receives first consideration, and the raw material of the fellmonger is usually cla.s.sified accordingly into "long wools," "short wools," and "mountain breeds." The skins vary very largely in quality of wool and in quality of pelt, being influenced very strongly by the conditions under which the sheep lived, and by the precise breed of animal from which the skin has been taken. As in the case of hides (Part I., Section I.), animals exposed to extremes of weather develop the best pelts, whereas those sheep which have been carefully bred and reared for the sake of their wool yield a thin and poor cla.s.s of pelt. In Britain, and more especially in England, are reared the finest and most valuable sheep.

This is evident from the prices paid for them by foreigners and colonial breeders when seeking new blood for their flocks and fresh stock for their lands. As much as 1000 guineas have been paid by an Argentine firm for a single Lincoln ram.

Long wools are obtained from some of the best and most extensively bred animals. The "Cotswolds" are the largest, and probably the original breed of England are still found on the Cotswold Hills. They have long wool, white fleeces, white faces, and white legs, and have no horns. The wool is fine, but the pelts are particularly greasy, especially along the back. A later breed originating in the Midlands was called the "Leicester" long wool. This breed gives a great cut of wool and much coa.r.s.e mutton. It is very extensively distributed in the North of England and has been much crossed, so that many sub-breeds are now well known, _e.g._ the "Border Leicester"--the general utility sheep of Scotland--and the "Yorks.h.i.+re Leicester" or "Mashams," much bred in Wensleydale. "Lincolns" are another long wool found only on the Lincolns.h.i.+re Wolds. They also have white faces and shanks and yield a large pelt with fine grain. They give a big crop of wool. "Devons" are a smaller breed common in Somerset, Devon and Cornwall. They yield a fairly long wool of great strength, but not quite white. Romney Marsh sheep ("Kents") are also long wools. They have white legs, white faces, a tuft of wool on the head, and no horns. The pelt is large and good.

"Roscommons" are an Irish cross breed with much Leicester blood. They yield a long wool and a spready pelt.

Short wools are typified by the "Down" sheep. These sheep are extensively bred on the chalk lands which comprise a very large percentage of the southern counties of England. The "South Downs" are the best and most important, the breed being the general utility sheep of England. They are small but well-shaped animals with grey faces, no horns and fine close wool. The pelt is only fair, but the mutton is excellent and provides the meat sold in our best shops. This breed has largely stocked New Zealand. The "South Down" is a somewhat delicate animal, and has therefore been largely crossed with Cotswolds and other breeds. Many well-known cross-breeds are found in the eastern and southern counties. The "Suffolks," for example, are found in the eastern counties. They have black heads, faces and legs. "Oxfords" and "Hamps.h.i.+res" are similar, but larger. "Shrops.h.i.+res" are another hardy cross-breed, which yield a heavier fleece. All the cross-breeds are larger than the South Down and yield bigger pelts.

Mountain breeds yield wool of varying quality but give the best pelts.

The "Cheviots"--much favoured by the Scotch farmers--have a wool of medium length but with much hair in it. They have white faces and legs and no horns, and yield excellent pelts. The "Black-faced Mountain Sheep" have longer wool but coa.r.s.e, and yield good pelts. They are kept in the hilly parts of North England and in the Scottish Highlands.

"Lonks" yield a large and good pelt, but very coa.r.s.e wool. The mutton is good. They are a very large breed with much curved horns and black faces. There are also some small breeds, "soft wools," "Shetlands," and "Welsh Mountain Sheep." The wool of the last two is poor, but the Welsh pelts are valued for their fine grain. There are large numbers of sheepskins also imported, from South and Central America, and from Australia, New Zealand and the Cape. The colonies, however, have often done their own fellmongering, and we have imported pickled pelts. They now tan the skins also, and many tanned sheepskins are now imported.

There are also many Indian skins imported after tannage with turwash bark (cp. E.I. Goat, Section II.).

The depilation is brought about by "sweating" (or "staling") and by "painting." The immediate object of both these types of method is to avoid using any thing which will affect the wool. The sweating process is the most ancient method of unhairing and is used in America for hides as well as sheepskins. It consists of a more or less regulated putrefaction. The loosening of hair or wool has long been accepted as evidence that putrefaction had commenced in a hide or skin, and it is the aim of the sweating process to stop the action at that stage, before any damage has been done to the pelt. This aim is achieved rather imperfectly by suspending the goods in closed chambers and regulating the temperature and humidity by means of steam and water. Such chambers are known as "sweat pits" or "tainting stoves". In the case of sheepskins the "warm-sweat" system is generally used, and the operation is carried out at 75-80 F. A satisfactory yield of wool is obtained in good condition, but the pelt is very liable to suffer bacterial damage and show "weak grain." The skins are first cleaned by a few "soaks" in clean fresh water, with intermediate help from a "burring machine" which presents a rapidly revolving set of spiral blades to the wool, and in the presence of a good stream of water quickly removes all dirt from the wool. The skins then enter the tainting stove, and the operation is commenced by a slight injection of live steam. In summer, about a week is sufficient to loosen the hair, but in winter up to two weeks may be necessary. Little control of the process is possible, and all that can be done is to watch the goods carefully near the end of the operation.

In one variety of this method of unwoolling the skins are painted on the flesh side with a creamy mixture of lime and water and piled for a day or two until the pelt is distinctly plumped. They are then washed with fresh water to remove the excess of lime, drained, and then enter the tainting stove. By this method the pelts are obtained in better condition and are less liable to damage by local excess of putrefaction.

In unwoolling the skins are placed over a beam and the true wool is pulled out by hand. The wool is graded as it is pulled and different qualities kept separate: ewe wool, lamb wool, hog wool, etc. The hair is next removed from face and shanks by means of a blunt "rubbing knife,"

and the pelt then immersed in water.

In the other method of depilation, by painting, advantage is taken of the loose texture of the sheepskin fibre and of the fact that the wool root is nearly halfway through the skin. The flesh side of the clean skin is painted with a creamy mixture of lime in a strong solution of sodium sulphide (14-24 Beaume). Care is taken to keep the depilatant off the wool. The skins are folded flesh to flesh and left for a few hours or until next day before unwoolling, according to the strength of the sulphide solution. The depilatory action is entirely chemical, being due to the solvent action of the sulphide on the hair root. The lime is sometimes omitted. After pulling, the skins are opened up and washed in fresh water.

The various cla.s.ses of wool are sold to the wool-stapler and so to the woollen industry. As this is a mechanical rather than chemical industry, its discussion is beyond the scope of this volume. However unwoolled, the pelt still needs further treatment by the fellmonger. It needs liming and unhairing. This is done in the ordinary way in pits of milk of lime, through which the goods pa.s.s from old to new limes in the course of about a week. This plumps the fibres, separates the fibrils and kills the grease. Paddles are used also to save handling. Shearlings are sometimes limed 9-14 days and unwoolled without sweating or painting. After liming the skins are unhaired and fleshed, and placed in clean strong limes until sold to the tanner.

Sheepskin pelts are sometimes preserved by pickling. This consists in placing them first in a solution of sulphuric acid (about 3/4 per cent.) together with some common salt. The pelts swell up and imbibe the acid solution. They are then placed in saturated brine, which causes a very complete repression of the swelling, the pelts being apparently leathered. In this condition or partly dried out they may be kept for years. The forces at work in this phenomenon are somewhat complex (see Part V., Section I.). The skins may be depickled by paddling in a 10 per cent. salt solution to which weak alkalies such as borax, whitening, carbonate and bicarbonate of soda, etc., have been added.

The leather manufacturer cla.s.sifies sheepskins according to the size of the pelts. The large skins are tanned for light upper leathers and similar work. These are called "basils." Many large skins are also split green into "skivers" which after vegetable tannage are finished for fancy goods, bookbinding, etc. The fleshes are often oil-tanned for chamois leather (Part IV., Section III.). Medium-sized skins such as are obtained from the Down sheep are tanned for "roans," and finished as a kind of morocco leather. Small skins are mostly "tawed" (Part IV., Section I.) for glove leathers, but some are made into roller leather by vegetable tannage.

Basils, which represent the heaviest sheepskin work, are tanned and finished in the following manner. The limed pelts are first bated lightly at about 80 F. for two days, scudded and drenched. They are sometimes puered, but more often merely delimed with organic acids. In this last case they are first paddled in warm water to remove excess of lime, and a mixture of organic acids is very slowly added at definite intervals. When nearly free from caustic alkali the skins are removed and drenched overnight. There are two types of tannage. The West of England tannage is similar to those noted for sealskins when oak bark and sumach are employed (Section III.). There is also the tendency to paddle more and handle less, and to use the stronger tanning materials such as myrabs, gambier and other extracts. After about 12 hours'

tannage in paddles they are coloured through, and are then degreased by hydraulic pressure. The skins are piled in the press with layers of sawdust or bran between them, and the pressure applied very slowly. Much grease runs out, for the natural sheepskin contains up to 15 per cent.

of oil and fat. Degreasing may be postponed till tannage is complete, and the grease can then be extracted by solvents (benzene, acetone, etc.). Degreasing after part tannage is usually considered preferable, and the skins may be tanned out in pit or paddle in about a week. The Scotch tannage is with larch bark from _Pinus larix_, which contains up to 13 per cent. of a rather mellow catechol tan. This material has also some sugars and yields sour and plumping liquors. The basils are paddled in weak liquors (8-11) for about 2 days, and when struck through are degreased by hydraulic pressure. They are then soaked back and tanned out in stronger liquors (11-20), which takes up to one week. They are then dried out and sorted in the crust. The finis.h.i.+ng depends of course upon the purpose in view. If for linings they are soaked, shaved, sumached, struck out well, nailed on boards and dried right out. They are next stained with a solution of starch, milk and red dyestuff. After drying they are glazed by machine and softened with a hand board. For fancy slippers the crust skins are starched and stained directly, then "staked" (see Part III., Section II.), fluffed, seasoned and glazed. If intended for leggings and gaiters a flesh finish is given. The skins are soaked, stretched, shaved and sumached. They are then rinsed, drained, sammed and stained. A brown stain mixed with linseed jelly is usual.

This is spread evenly over the flesh and gla.s.sed in. The skins are dried out, restained if necessary, and staked to raise a nap. Basils for gaiters are dyed in paddle and fluffed over the emery wheel.

Skivers are split in the limed state and sometimes immediately degreased. They are next puered at 85 F. for about 3 hours in a paddle, and scudded. They are drenched at a low temperature (68-70 F.), but often 2 or 3 days. They are again scudded and then rinsed and sent to tan. The skivers are tanned in a few days by sumach liquors working the goods up from mellow to fresh as usual. The liquors are warmed. Care must be taken that the goods do not tear. A great variety of finish is possible, but the "paste grain skiver" for fancy goods and the plain finish for hat leathers are sufficiently typical. For paste grains they are soaked and "cleared" for dyeing by immersion in very weak sulphuric acid, excess of which is carefully washed out with water. Paddle-dyeing follows, and is preferred to drum dyeing as the skins are so liable to tear. After being struck out they are "pasted," by spreading on to the flesh a glue jelly, using first the hand, then a stiff brush and finally a cloth. The goods are then dried out. They are then seasoned, partly dried and printed cross-grain. They are next grained two ways lightly; shank to shank, and across, lightly tooth-rolled and glazed. They are regrained two ways as before, dried out, and finally softened with a graining board. They are sometimes sized on the grain to fix the pattern and give a gloss. For hat leathers the skins are first soaked, sumached and struck out. If for white or cream finishes they are now lead-bleached. This consists of pigment dyeing with lead sulphate. They are immersed alternately in lead acetate and in sulphuric acid solutions until precipitation is sufficient. They are then dyed to shade. If for browns it is common to mordant with t.i.tanium and use basic dyestuffs, paddling afterwards in sumach to fix the dye. After dyeing the goods are struck out again, starched, and dried out on boards. They are again starched and rolled to give the plain finish.

Roans are not split. They are degreased, puered, scudded and drenched overnight at 95 F. They are tanned with sumach usually in pits, and take rather longer than usual to tan. They are finished in much the same style as goatskins for morocco leather, but as the sheepskin has little natural grain it needs embossing or printing according to the type required. If for "hard grains," the skins are soaked, sumached, seasoned, dried, glazed and damped back for printing. This is done by the "hard grain" roller, and the goods are dried out to fix the pattern.

They are damped back, sammed, and grained in four directions (cp.

Section II.), dried out and boarded to soften. If for straight grains they are printed with a straight-grain roller, or grained neck to b.u.t.t.

After tooth rolling they are boarded, dried and glazed. They are softened down and "aired off" in a cool store.

Roller leather is a special cla.s.s of sheepskin leather which is used to cover the rollers used in cotton spinning. The essential requirements are that a smooth plain finish should be given, and the leather must not stretch or be greasy. For this purpose small sheepskins with a fine small grain are chosen, such as those obtained from the Welsh mountain sheep. The pelts are machine fleshed, short haired and often puered, but the deliming is also brought about by organic acids also. The pelts are drenched in pits fitted with paddles, which are used to stir up the infusion occasionally. A thorough scudding is given. For the smooth-grain finish it is necessary to tan in weak liquors, and to give plenty of time so as to ensure complete penetration. An oak-bark tannage is preferred, but a little extract is usual to a.s.sist. The goods are coloured through in paddle, like basils, and are then degreased by hydraulic pressure. This should be as complete as possible, and a little heat is used to a.s.sist the escape of grease. The pressed skins, moreover, must be quite freed from creases, and this is attained first by paddling in warm water to remove sawdust, and then by drumming in fairly hot water, in which they are left overnight. The skins are tanned out in suspenders, taking about 3 weeks. The crust skins need careful sorting, and are soaked and hand shaved. They are sumached in drum, rinsed, struck out, sammed and set. The striking and setting should be thorough, in order to get rid of stretch. They are next "filled" by coating with linseed jelly or similar material, and dried out on boards in a thoroughly stretched condition. They are then trimmed, seasoned and rolled with a steel roller. They are then staked or perched, fluffed, reseasoned, dried and glazed. They are carefully short-haired, glazed again and finally ironed.