Chapter X: Section VII: Harness Leather

When discussing the question of oak bark (Section III.), reasons were advanced for its decreased use and popularity. These were quickly appreciated in the sole leather trade, but the obsolescence of oak bark in the dressing-leather section was much more prolonged, partly because there was less pressing need to obtain good weight in the actual tanning, and partly because in some branches of dressing leather, such as belting and harness, a leather was required of great durability and toughness, for which qualities oak bark tannage had a deservedly high reputation. Hence harness leather manufacture affords a good illustration of the transition between the methods of the late nineteenth and those of the twentieth century. With the use of oak bark lingered the old methods of liming, bating and tanning in weak liquors for a long time with plenty of gambier. Hence in this section it will be necessary to observe a gradual transition of method, both in wet work and tanning. It should be pointed out that this transition has not been and is not going on in all factories at the same rate. Many factories remain in which the old methods are still preferred at some stages of the manufacture, and some remain in which many of the changes indicated below have not taken place at all. The leather trade has always been considered conservative in its methods, but it should be realized that much of the prejudice in favour of old methods is due to the public, and that after all tanners and curriers, like other business men, have to suit their customers. The march of industry is not like a regiment in line; it is rather more like nature, a survival of the most adaptable.

Hides for harness leather are limed in various ways, of which the following are types.

1. A rather mellow liming of 10-15 days (longer than for sole leather), in which nothing but lime is used, and a certain amount of old liquor used in making up the new limes. The liming was carried out by the one-pit system, but the goods and liquors were kept clean by a good soaking process. Hence the loss of hide substances was not very great; goods so treated were bated before tanning.

2. A shorter liming than the above by the three-pit system. This saved time (taking 9-10 days), saved hide substance, and ensured greater regularity of treatment. The limes were about as mellow, but a little sulphide (2-4 ozs. per hide) was used to assist the depilation, especially during the short-hair season. These goods were also bated.

3. A distinctly longer liming, 15-16 days, in mellower limes. This differed from Type 1 also in the respect that greater regularity was ensured by the three-pit system; a foot or two of old liquor was used in making up the new lime. More hide substance was lost than in either of the above processes, but this was deliberate, the object being to dispense with bating, which is always light for harness hides. Thus a longer and mellower but systematic liming was used as a substitute for shorter liming and bating. No sulphide was used in this process.

4. A short liming of 6-7 days, using up to 12 ozs. of sulphide per hide. The object here is to save time and hide substance. The three-pit system is preferred. Bating again becomes necessary, but the pigeon-dung bate is replaced by artificial bates, less objectionable, quicker, and more scientific in management.

5. A still shorter process of about five days, using still more sulphide (about 16-20 ozs. per hide), together with some calcium chloride to reduce harshness. In such a method there is a tendency to revert to the one-pit system, which involves rather less labour. The three-pit system shows to a great advantage in the longer processes of liming when the process is reduced to five days; there is little difference between the two, for a one-pit system is a two-liquor method. Hence again an artificial bate is used.

The various methods of liming, together with analogous variations in tannage, have resulted in great variety in bating. Sometimes up to three days' bating has been given at 70° F., but more often the goods are merely immersed overnight, and then delimed with boric acid, but with sulphide processes it is an advantage to use some of the commercial bates of the ammonium chloride type, and finish off with boric acid. Scudding is always more thorough than for sole or belting, the hides are rounded into long butts which include most of the shoulder "harness backs." The goods are sometimes bate shaved.

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

=Type 1= may be taken to represent the so-called "high-class" 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 pass 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 pass 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 class 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 classification. 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 assists 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 coarser 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, scraping, 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, glassing 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 glassed during the finishing.

REFERENCE.

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