Section IV Sheepskins
The most numerous class 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 principal 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 constituent 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 classified 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., p. 8), 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 class 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 coarse 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 “Yorkshire Leicester” or “Mashams,” much bred in Wensleydale. “Lincolns” are another long wool found only on the Lincolnshire 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 “Hampshires” are similar, but larger. “Shropshires” 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 coarse, 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 coarse 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., p. 100).
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° Beaumé). 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 classes 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 pass 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 ¾ 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., p. 200). 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 classifies 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., p. 181). 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., p. 174) 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., p. 108). 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 finishing 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., p. 155), 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 glassed 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 titanium 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., p. 104), dried out and boarded to soften. If for straight grains they are printed with a straight-grain roller, or grained neck to butt. 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 class 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 assist. 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 assist 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, re-seasoned, dried and glazed. They are carefully short-haired, glazed again and finally ironed.
E.I. sheepskins are imported in a tanned condition. These are soaked back and the turwar bark tannage “stripped” as far as possible by drumming with soda for 20-30 minutes at 95° F.; after washing they are “soured” in weak (½ per cent.) sulphuric acid solution, and retanned with sumach paste for an hour, drumming at 100° F. They may then be finished for basils, moroccos or roller leather as described above, but are often finished as imitation glacé kid. In this case they are drum dyed, lightly fat liquored (see Part III., Section IV., p. 163), struck out and dried. They are staked by machine, fluffed, seasoned and glazed. They may be re-staked and reglazed if desired.
REFERENCES.
A. Seymour Jones, “The Sheep and its Skin.”
Bennett, “Manufacture of Leather,” pp. 30, 85, 107, 208, 349-354, 385.