Animal Proteins Part 6

A few tannages will now be outlined, in order of historic type.

=Type 1= may be taken to represent the so-called "high-cla.s.s" process in which oak bark myrabs and valonia are the staple materials. A good deal of gambier is also used, and a little myrabs and chestnut extract are helpful in attaining the desired strength of liquor. The "backs" go first through suspenders (8-30), which takes up to three weeks, and then in to handlers (30-40) for four weeks, consisting of rounds of clear liquor. They next go through a duster round, in which they are put for a week with oak bark and myrabs into a liquor of 45. Four layers are given (50, 55, 60 and 65), in which the goods remain for two, three, four and five weeks respectively, oak bark being the chief dusting material. The tannage is thus for twenty weeks. Light backs receive less time in the layers (only 11 weeks). If the tanner is also the currier, the fourth layers are omitted. He then saves five weeks and gets the weight in the stuffing.

=Type 2= is a tannage in which oak bark and valonia are replaced by myrabs, mimosa bark and chestnut extract. It is therefore considerably cheaper and probably no less durable. Expense is also curtailed in handling. The harness backs go through suspenders (16-30) in two weeks, handlers (30-45) in four weeks, and then receive four layers of the same strength as in Type 1, but only one, two, three and four weeks respectively. The last layer is omitted for light harness, and an extra layer of 75 is given if the tanner is not the currier also. Thus the usual tannage is 16-20 weeks, of which 10-14 weeks (63-73 per cent.) are in layers.

=Type 3= is a tannage which may consist of myrabs (55 per cent.), valonia or mimosa bark 25 per cent., and extract (26 per cent.). The extract is chiefly quebracho, though some chestnut may be used. More valonia and less myrabs may be used if desired (and when possible), and myrabs extract will then replace quebracho and chestnut. The goods are coloured off in drums or paddles, and then pa.s.s through two sets of suspenders handlers (20-55 and 55-75). They are handled up and down very frequently in the first set and rapidly pa.s.s into stronger liquors.

The backs then receive three floaters at 80, in each of which they remain one week. The tannage is completed by three layers: first, 85 for one week; second, 90 for one week; third, 95 for two weeks. The tannage is thus 11 weeks, of which 7 weeks involve little labour. If the tanner is not the currier, still stronger liquors may be used.

In all these tannages little or no acid is used for plumping, as the natural acids of the liquors are sufficient to ensure what is necessary in this direction for this cla.s.s of leather. A little organic acid or even boric acid may be used in the earliest liquors for deliming purposes, when necessary. After tanning the goods are dried out and sorted in the rough state. Harness is a somewhat broad term, and there is scope for considerable variety in cla.s.sification. The hides are sometimes not rounded until after tanning. The finished article may be any grade between heavy harness for artillery and leather for ordinary bridles.

In currying heavy black harness, the backs are soaked and sammed for shaving. Lighter goods may be machine-shaved, but the heaviest are shaved lightly by hand over the beam or merely "skived" with the shaving slickers. The neck needs most attention, and it is often advisable to stone by machine and split. The scouring should be thorough, on flesh and grain. This is done by machine, and not only cleans the goods from bloom, dirt and superfluous tan, but also a.s.sists in setting out.

Sumaching may be for several days, merely overnight or even only for a few hours, being stoned after wetting back to temper. Hand-stuffed goods get a coat of cod oil first, and during the drying are often well set out. Drum-stuffed goods are well set out by machine, and after some drying, stoned and reset by hand. It is now usual to buff the grain, _i.e._ remove the coa.r.s.er parts by light shaving. This prevents cracking in the finished article. The goods are blacked with logwood, iron and ammonia, thinly dubbined again, again well set out and tallowed. Setting out, indeed, may be done at any convenient opportunity. The superfluous grease is removed by slicking, sc.r.a.ping, brushing with a stiff brush, and finally with a soft brush.

For brown harness the goods are more carefully selected, more thoroughly scoured and sumached, and bleached frequently with oxalic acid. They are hand stuffed, stained twice, and after the usual setting out, gla.s.sing and brushing, are finally rubbed with flannel.

For bridle leather the goods are carefully shaved but are not stuffed, being merely oiled with cod oil on flesh and grain. They are dried out before scouring, and then sized, set out, stained and resized. The goods are heavily gla.s.sed during the finishing.

REFERENCE.

Bennett, "Manufacture of Leather," pp. 195, 297.

Section VIII.--UPPER LEATHERS

The manufacture of leather for the uppers of boots and shoes embraces a bewildering variety of goods, suitable for anything between a baby's shoe and a man's shooting boot. Almost all degrees of lightness, softness, and waterproofness are in demand. A great variety of finish is also involved, determined by the ingenuity of the currier and the ever-changing fancy of the public. Even greater is the variety of methods by which all these results are obtained by methods which superficially seem quite different; the desired qualities being imparted in one case largely by the tannage and in another case almost entirely by the currying. Under such circ.u.mstances the selection of types becomes a problem.

The variety, moreover, commences from the earliest stages, the selection of the raw material. Upper leather may be made from light calfskins, heavy calfskins, kips (home and foreign), light dressing hides and heavy dressing hides, which last may replace any of the former after splitting to the required substance. In this section it will be necessary to take kips as typical of the rest, and to use it in a rather broad sense, including heavy calf and light dressing hides.

Speaking quite generally, kips for upper leather receive usually a long and mellow liming, a thorough bating and a sweet and very mellow tannage in weak liquors. In currying they are well scoured and set out, heavily stuffed and stained black, being sometimes finished on the grain and sometimes on the flesh. These outstanding features of upper-leather methods will be further ill.u.s.trated by a brief account of the tanning of kips (light hide and heavy calf), and outlining the best known types of finish for b.u.t.t, shoulder and belly.

The goods receive usually a long and mellow liming of 14-16 days, using only lime as a rule. In some factories lime liquors are used repeatedly for successive packs to an almost indefinite extent. Dissolved hide substance, ammonia, mud and dust, and bacteria acc.u.mulate for months and sometimes for years. It is obvious that in such liquors "putrefaction"

is a more correct term than "liming" for the depilation. Such methods have been used even in recent years, but there has now been a tendency for some time to make the liming more methodical. Such old limes make a leather which is empty, loose, and dull grained, but the defects are minimized by the system of stuffing heavily and finishing the flesh, and hence the ancient lime remained with surprising tenacity. Even so late as 1903 we find that Procter with characteristic caution could write, "Probably no lime ought to be allowed to go for more than three months at the outside limit without at least a partial change of liquor." It is within the writer's experience to find an upper leather factory with limes which had never been emptied for over three years. In other factories, however, there has been a revulsion of feeling with regard to such processes, and it has been found advantageous to adopt a more scientific routine, in which the lime pits are cleaned out at regular intervals. There is little doubt that a mellow liming is desirable, but this can be secured by blending some old lime liquors with fresh lime liquor in a systematic manner. Similar considerations apply to the question of working the various packs through the limes. It is clear that with a mellow liming a one-pit system is quite possibly satisfactory, but the revulsion of feeling against a lack of method produced a method of liming more elaborate than usual, and it is now not uncommon to find kips limed in a "round" of 6-8 pits, the goods pa.s.sing through each pit. They remain in one pit about two days, and are shifted forward. In the green or old limes the goods are handled up and down.

The old limes are, of course, mellower than the new and exert the desired softening effect. The working is quite a.n.a.logous to that of a round of handlers. Unhairing is sometimes a.s.sisted by the use of a.r.s.enic sulphide. E.I. kips need a thorough soaking before any liming; several days are usually needed. The old methods involving putrid soaks and stocks may be considered out of date, and it is usual to soften back in caustic soda or sulphide soaks with some a.s.sistance by drumming. A little sulphide is sometimes added to the older limes to continue the treatment.

The goods are next thoroughly bated and delimed. The hen or pigeon dung bate is still usual, and probably gives the best results, though closer approximations have been made of recent years on artificial lines. Some bating with solution of hide substance seems necessary for these goods.

The lighter goods are often drenched also to complete the deliming, using 6 per cent. bran on the weight of pelt. The heavier goods are more often treated with boric acid after bating, which not only delimes completely and gives a soft relaxed felt, but also acts as antiseptic and stops the action of the bate, a matter of some importance (see Section II.). Lactic acid may subst.i.tute boric, in which case about 2 per cent. on the pelt weight of 50 per cent. acid may be required. It is important to avoid a strong solution and local excess, hence lactic acid must be added gradually so that the liquor is never stronger than 0.2 per cent. Drumming and paddling is an advantage in deliming.

The tannage is light in most cases, partly because some of the finished goods are sold by area, but partly also because even if sold by weight, the weight is obtained quicker and more easily by stuffing, which course is also often preferable to obtain the desired mellow feel, waterproofness and durability. Hence it is seldom that strong liquors are employed. The tannage is also mellow, on account of the softness and pliability required; no acids are consequently employed, and no material which is liable to yield sour liquors. Gambier is easily the first favourite amongst the tanning materials, whilst oak bark comes second.

It should be observed, however, that a hypothetical tannage of equal weights of cube gambier and oak bark is in reality a tannage by four-fifths gambier and one-fifth oak bark, on account of the relatively greater strength of the former. This observation is so apposite with respect to some tannages that it is nearly correct to say that the tannage is gambier and the oak bark an excuse for having leaches through which the gambier liquors may be run occasionally to clear and to sharpen slightly. No serious theoretical objection to such a method is possible if the liquors are weak and the system of working the liquors is scientific and the process carefully regulated. Upper-leather tannages, however, have scarcely merited scientific praise. It is often a case, not of poor methods, but of no method at all. The same lack of system, principle, and regularity observed with regard to the limeyard has been equally obvious in the tanyard, when perhaps the need was even greater. Even a mellow tannage has varying degrees of mellowness possible to it; there still remains the question of the soluble non-tans. However, method in the upper-leather tanyard has often been conspicuously absent. There has been many a factory where any one tan liquor was as good as any other in the yard. In the writer's experience are two such cases: in one the liquors were all 25 Bkr., in the other they were all 0 Bkr. In such cases, handling the goods from pit to pit is somewhat futile, and handling forward from set to set still more so.

Hence it is possible to find dressing leather tanned by putting it slowly through one round of handlers, adding a few buckets of gambier where it apparently is necessary. It is, from one point of view, surprising to see what serviceable and excellent-looking upper leather can be manufactured by such happy-go-lucky processes. It is, however, also possible to see how this may occur. Gambier is a stable tan, and no souring and little decomposition take place in gambier liquors. It is also extremely mild and non-astringent, and is always used in weak liquors. The hides, moreover, are completely delimed, and there is little danger of bad or uneven colour. Tanning under these conditions is at its easiest; it is almost more difficult to spoil the goods than make them right. Under such conditions tanning deteriorated rather than improved in method. When neglecting it made little difference to the finished leather, it was neglected.

This state of affairs, however, was embarra.s.sing whenever a tanner wished to try any other tanning material. The expense of gambier and oak bark made valonia and mimosa bark into obviously desirable alternatives and subst.i.tutes. Methods which would tan with gambier, however, would not work with Natal bark or valonia, and many a tanner has had to revise his method of tanning from end to end. The use of myrabs also raised the problem of souring, and it has become evident that "working the liquors down the yard" is as desirable a method for dressing leather as after all other tannages. It will be clear from the above that types of upper-leather tannages are less typical than for other leathers, but nevertheless the more progressive manufacturers have for some years now been working on sounder lines, economically and scientifically. In such cases it is now usual to pa.s.s the goods through at least two sets of handlers, and through liquors of gradually increasing strength.

Occasionally dusters or layers are given, especially for the heavier goods. The tannage is nearly always commenced now by paddling the goods in the oldest liquor. This paddling may be anything from half an hour up to twenty-four hours. It is sometimes desired to work up a "grain," and the old liquor is then often sharpened by the addition of fresh gambier or leach liquor.

The same tendency to save labour in handling is to be observed in upper leather tannages as in sole and other dressing leather factories. There is also a tendency to obtain rather more weight in tanning by using stronger liquors, and in the heavier goods to shorten somewhat the time taken. The following methods may be taken to ill.u.s.trate modern processes, in order of evolution. They all last about seven weeks.

_Type 1_.--In this process the kips are first paddled in an old liquor (3), and pa.s.sed to the first handlers (3-30) for three weeks. After working through this set they pa.s.s through the second handlers (20-30), in which they are not handled quite so frequently. They are in this set also three weeks. Heavy goods may then receive a floater (30) for another week.

_Type 2_.--In this process the goods are paddled, and then enter a large handler round (8-30), through which they pa.s.s in five weeks. The goods are handled frequently in the early stages. The tannage is completed by one layer of two weeks (30). The layer is made by the ancient method of putting the goods and dust alternately into an empty pit, and then filling up with liquor from the best leach. Oak bark, valonia and myrabs are used as dust, though sumach and gambler have been used.

_Type 3_.--In this process an attempt is made to save handling and obtain more complete tannage. The goods are paddled for three to five hours in a rather sharp liquor of 10, and are then handled well for a week in the first handlers (5-20). The goods then go through the second handlers (20-45) in six weeks, and heavy goods may then receive an extra floater (45) for one week.

In type 1 the leaching material is two-thirds oak bark and one-third valonia; in type 2 it is half oak bark and half mimosa bark; in type 3 it is one-third oak bark, one-third valonia or Natal bark, and one-third myrabolans. In all cases the strongest handler is obtained from the leaches, and made up to the required with strong infusion of gambier.

When the liquor has pa.s.sed through the forward handlers, it is returned to the leaches to clear and sharpen, and then run to the green handlers.

After pa.s.sing through this round it is returned to the paddle, from which it pa.s.ses to the drain. The rest of the paddle liquor may be from the forward handlers. It is often customary to obtain the best liquor from the second leach, and allow the best leach to stand for a few days.

This allows the bloom to deposit in the leaches. The system secures the result desired, but the deposition of bloom involves a loss of tannin, which waste makes the system expensive.

Heavier dressing hides are tanned by methods similar to the above, but with floaters, dusters and occasionally layers added after they have pa.s.sed through two sets of handlers. Thus they may have first handlers (8-18) two weeks; second handlers (40-45) for six weeks, making twelve weeks in all. Lighter goods may receive two rounds, being two weeks in each.

After tanning, the kips are rounded usually into b.u.t.ts, shoulders and bellies, to which different finishes are given. The currying may be ill.u.s.trated by selecting types, but it must be borne in mind that there is much elasticity in this matter. Thus kips may be made into waxed b.u.t.ts, satin shoulders and lining bellies, but also may be cut down the back in "sides," both of which are finished limings.

Waxed kip b.u.t.ts are a type of many similar upper leathers (waxed shoe b.u.t.ts, waxed calf, waxed splits, etc.). The finish is on the flesh side.

The kip b.u.t.ts are soaked carefully, and shaved by machine. They are then drummed in sumach for an hour or two, slicked out and sammed for stuffing. The sumaching is also the scouring unless the goods be too heavily bloomed. The samming is often done by machine. Drum stuffing follows, wool fat and stearin being staple greases, with varying amounts of degras and cod oil, and of tallow and cod oil. A little paraffin wax and resin are also used sometimes. The goods are well slicked out and dried. They may be now dubbined and laid away to mellow for whitening, which consists of a careful shaving of the flesh by a turned-edge slicker or by machine. The grain is stoned, set out and "starched," and the b.u.t.ts grained by boarding the flesh. In the waxing, one of two courses may be adopted. The b.u.t.ts may be blacked with lampblack and oil, "bottom sized" with glue, soap and logwood, and then "top sized" with glue, dubbin, beeswax and turpentine; or they may be given a "soap-blacking" of soap and logwood and lampblack, applied by machine, and sized once only.

Dressing hide b.u.t.ts may also be given a grain finish, such as the "memel b.u.t.ts" for heavy uppers. The b.u.t.ts are soaked, shaved or split, sumached in drum, and preferably thoroughly scoured on flesh and grain. They are then sammed and heavily stuffed in the drum. The grain is buffed and stained black with logwood, ammonia and iron solution (curriers' ink).

The b.u.t.ts are then dried, set out, thinly sized and slowly dried.

When dry on the face they are printed or embossed by machine to give the characteristic memel pattern and dried out completely. They are then grained four ways. The grain is finished by a coating of linseed oil containing resin, and the flesh is whitened, French chalked and gla.s.sed.

Shoulders for "satin" receive a currying which strongly resembles the "waxed" finishes, but the smooth finish is on the grain side. The grain is buffed, and blacked, dubbined, set and reset, with intermediate drying, and is sized and finished by compositions similar to those used for waxed leathers. The flesh is whitened. Satin hide and satin calf are dressed similarly.

Shoulders may also be finished for "levant." After soaking, splitting, and shaving to substance, they are drum-sumached, machine-sammed, and oiled up to dry. They are stained with logwood on the grain, and at once printed with the typical "levant grain," blacked and dried out. They are then softened by machine, seasoned with logwood and alb.u.men, glazed, grained and oiled lightly with mineral oil. It will be observed that stuffing is omitted.

Bellies may be dressed for linings. After soaking and splitting to the required substance, they are bleached in a weak and warm solution of oxalic acid, and drum-sumached at 110 F. After slicking well out they are hand-stuffed on the grain with dubbin and water, or merely oiled, and hung up to samm. They are then set-out flesh and grain. If the grain be coa.r.s.e, it is buffed and reset. After drying out the flesh is fluffed and the grain dusted with French chalk.

In this section may be conveniently discussed the manufacture of legging leather. Whilst in many respects a typical dressing leather there are some rather important differences from the average upper leather.

Broadly speaking, the differences are that legging leather needs a smooth grain, greater firmness and more thorough tannage on account of the absence of stuffing.

The liming and bating are somewhat similar to dressing leather, though a shorter liming with sulphides and a milder bating would be in order. The tannage is mellow, but not so much as is usual for upper leather. Thus gambier is used, but more valonia and myrabs are employed, and the liquors may be strengthened with chestnut and quebracho extracts. The hides are rounded before tanning into long b.u.t.ts or backs, and the tannage is commenced in suspenders (18-40), which are kept acid by the addition of lactic or acetic acid, in order to obtain the required firmness; the goods are three weeks in these liquors. The backs next go through rounds of dusters (40-50), in which they are put down with oak bark and Natal bark. They are six weeks in this section, and then pa.s.s to the layers. Three layers are given, first 50 for one week; second 55 for two weeks; and third 60 for two weeks. The tannage thus takes fourteen weeks.

In finishing, the goods are soaked and split, and then scoured flesh and grain. They are heavily sumached, slicked out thoroughly, oiled up with linseed oil and dried out. They are then next damped back, stoned and flatted. After further wetting and tempering they are dressed with Irish moss and tallow on the flesh, and with gum tragacanth on the grain.

They are gla.s.sed whilst drying out, and then stained twice and gla.s.sed again. They are again brushed, seasoned and gla.s.sed by machine.

REFERENCE.

Bennett, "Manufacture of Leather," pp. 197-201 and 301-308.

SECTION IX.--BAG LEATHER

Hides to be tanned for bag leather receive a treatment which is little different in fundamental principle from that of dressing hides for upper leather, except that the tannage is usually shorter. Hides for bags and portmanteaux represent a type of dressing leather in which the outstanding features are that the goods are split but not rounded. The splitting is done at all stages, according to the requirements of the tanner. Some tanners split "green," _i.e._ split the pelt itself. The advantage of this is that the fleshes may then be treated in quite a different way, _e.g._ pickled or given a much cheaper tannage. Other manufacturers split after tanning, the advantage being that there is much less material to handle. The general opinion, however, favours a middle course in which the hides are split after being in the tan liquors for a short time. The advantage of this course is that the hides are easiest to split under these conditions--a great consideration--being coloured through with tan, just a little plumped, but not hard. A smoother flesh is obtained together with more even substance. Here again, however, are differences; some tanners prefer to split after two days, others after two weeks in tan. Much depends upon the nature of the tan and the strength of the liquors.