In the forward handlers, dustings of ground bark or other tanning material are very frequently given, and the layers only differ from these in having much heavier dusting, stronger liquors, and being allowed to remain undisturbed for greater lengths of time, ranging from a week up to a month or even six weeks, as the tannage progresses. The handler-liquors are principally from the old layers, though they are frequently made up with weak liquors from the leaches, and strengthened with extracts or gambier.
Very varied materials are used in the manufacture of sole-leather. Oak-bark is one of the oldest, and as regards quality one of the most satisfactory, but it is costly, not only on account of its weakness in tannin but from the light weight of leather which it gives. Valonia is one of the favourite materials, giving heavy weight and a solid leather, in which it deposits a great deal of bloom. Oakwood, chestnut-wood, and hemlock-bark extracts are now very largely consumed, principally in strengthening the layer-liquors; the great object being not only to lessen the cost in material, but to save time, and produce greater weight and firmness. The layer-liquors in some yards where extract is used, reach strengths of even 120° to 150° Bkr. (sp. gr. 1·12 to 1·15), while in pure oak-bark yards it is difficult to get above 30° or 35° Bkr.; and even these figures are only reached by repeatedly strengthening the same liquor, in which large quantities of non-tanning substances accumulate. The opinion of the most intelligent tanners is, however, that better results are attained by a regular change of liquor, even if the apparent strength is less.
When the leather has remained a sufficient time in the layers to have attained all the weight and solidity of which it is capable, it is washed up in a clear and somewhat weaker liquor or even in warm water, and taken into the shed to be dried and finished. As this finishing is almost purely mechanical, and scarcely comes within the scope of the present volume, a very brief sketch must suffice.
Fig. 39.—Wilson’s Striking Machine.
The mode of finishing which was formerly, at least, in vogue in Lancashire and Cheshire may be taken as a type of the best work. (In the present day, the various methods are so widely known that they have ceased to be local, and are varied according to the quality and tannage of the goods.) The butts, which in earlier times were largely bark-tanned, are taken wet from the pits, and scoured on a rounded beam or “horse” with stone and brush, till the bloom is completely removed, and are then lightly oiled on the grain, half dried (“sammed”), laid in pile to temper, and “struck out” with the “pin,” a two-handled tool of triangular section shown in [Fig. 29]. The use of this tool has now been largely superseded by Wilson’s striking machine [Fig. 39], in which knives or sleekers (or stones and brushes), held in jointed arms, are made to work on the butt, which is extended over a slowly rotating cylinder. The object of the pinning is not so much to remove bloom or dirt, which has been previously effected by the scouring, as to smooth and flatten the grain. After further drying, a second pinning is generally given, and the goods are then twice rolled, first with a light weight, and somewhat moist grain, and then more heavily with the grain nearly dry. This was formerly accomplished by a sort of box or car, heavily loaded with weights, supported on a smooth brass roller of about 5 inches diameter and 9 inches long, and manipulated with a long wooden handle on a floor of hard wood, or zinc plates. One type of the machines which have now almost entirely replaced this primitive contrivance is shown in [Fig. 40], but is principally used for offal and common classes of goods. For better work, traversing rollers, such as Wilson’s ingenious double bed roller shown in [Fig. 41], are to be preferred. After rolling, the goods are dried pretty rapidly by the aid of moderate heat, and, after polishing with a brush (hand, or machine, [Fig. 42]), are ready for sale. It may be pointed out that although the tools are different, the process is almost the same as that used for “vache lissée” in France and Belgium, and closely resembles that of currying harness leather except that the “stuffing” with fats and oil is omitted.
Fig. 40.—Offal Roller.
In contrast with the rather elaborate method just described, we may place the American finish of red hemlock sides, which are tanned throughout with a material which yields no bloom. On these, the scouring and “striking” is altogether omitted: the goods are completely dried out from the pits, which is found to fix the dark-coloured liquor, and result in better colour; they are then damped back, and tempered, and heavily rolled under a rapidly moving pendulum roller, which polishes at the same time that it smooths the leather. The saving of cost by so simple a process is not inconsiderable.
