REFERENCE.
Bennett, "Manufacture of Leather," pp 194, 295.
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.