Page:The American Cyclopædia (1879) Volume X.djvu/281

 LEATHEE 275 exercise of great care to prevent the tanning from going on too rapidly on the surface, de- pends the question whether a longer laying away in the bark liquor will add to the weight of the leather. The object in all sole-leather tanning is to get as great weight as possible, where this can be done without detriment. From dry hide about 170 Ibs. of leather are made of 100 Ibs. of hide ; in some cases the writer has seen 195 Ibs. of leather made from 100 Ibs. of hide ; but many poor tanners will make as low as 140 to 150 Ibs. In tanning green or wet hides, from 45 to 60 Ibs. of lea- ther for 100 Ibs. of hide represents about the average production. The common prejudice that quick tanning is necessarily poor tanning has no sufficient foundation. The best Eng- lish tanning, many years since, occupied from nine to 18 months, but the great majority of English tanners now tan in from four to six months. They are also, where valonia, divi- divi, myrabolams, and terra japonica are used, able to make good leather in even a much shorter time. The problem is to feed the tan- nin as quickly as possible, without too much expense, to every cell and interstice of the hide ; and by constant handling and agitation of the hide in liquors of the proper strength and proportioned to its condition, the work which formerly occupied months is now done in weeks, and could be done in days or even in hours if the extra expense incurred in this way were not greater than the profit to be de- rived from thus expediting the process. Among the many ways of quick tanning proposed, and which have found no small favor in the trade, are the vacuum process for sole and upper leather, and the revolving wheel or drum for upper leather and calf skins. The former pro- ceeds on the principle of pumping out the air, as from a receiver, from the vat in which the hides are placed, and then letting in the tan- ning liquors ; it is asserted that the pores of the hide are then more open, and the tannin will be more quickly taken up. The wheel or drum for upper-leather and calf-skin tanning is a DOX nearly filled with a strong tan liquor and the skins, and made to revolve on a shaft, thus constantly agitating the skins, and pro- ducing an opening of the pores which facil- itates the absorption of the tannin. Neither of these methods, however, has been generally adopted, though each has found favor and is used to a limited extent. After the leather comes from the last layaway vat, it is scrubbed with a coarse brush, operated either by hand or power, and hung up to dry. Care must be taken at this stage not to hang up the leather where there is too much light, which gives a dark color, and also to have as far as possible a constant circulation of dry air. After dry- ing, the leather is "sammied," as it is called, or slightly moistened and oiled on the grain side, by which it is brought to a flexible, mel- low condition, ready to be rolled or hammered, the final process of finishing. In America and England all sole leather is rolled, while in France and Germany it is generally hammered. The sole leather roller commonly used is of brass, about 5 in. in diameter and from 7 to 9 in. long ; it is hung like a pendulum over a solid metal bed with a concave face, in which the roller is worked by means of an arm at- tached near the lower end. The desired pres- sure is attained by means of a treadle which raises the bed. A rubber packing is sometimes used under this bed to prevent the pressure from coming too hard upon parts of the side or hide which may be naturally too thick or plump to receive the tremendous weight which can be brought upon it. In making belting and harness leather, where greater flexibility and the greatest possible tensile strength are sought, the methods of tanning are not essen- tially different. There is very little difference in the texture and appearance of leather which will wear best for the soles of boots and shoes, and that which will serve best for band leather ; and most of the heavy harness leather, if well stretched and finished with less oil or stuffing, would make good belt leather. But in the best belt leather, the original fibre of the hide must be as little disturbed as possible. An examina- tion with a microscope of the edge of an ordi- nary piece of sole or belting leather will show how these fibres are interlaced ; and, when not disturbed, this constitutes the great strength of a raw hide. In the tanning and finishing of harness leather, the object is to make the stock still lighter than belting leather, and also to give it much more body and strength than any leather which is to be used for the uppers of boots and shoes. With this end in view, the hides are kept longer in the lime, by which more of the gluten is exhausted, and a higher degree of care is consequently necessary to in- sure the thorough working out of the lime, which would cause the leather to crack, or be hard and brittle. In the tanning of upper leather and calf skins the time occupied is very much shorter than that used in making sole leather, and the processes embrace a great va- riety of methods of handling, agitating with a wheel, suspending in vats of tan liquors, &c. Greater care is necessarily taken in selecting and fleshing the skins ; and if the lime used to unhair is not thoroughly worked out, the leath- er will crack quickly. The currying consists in the thorough working of the skins to soften them, blacking, and thoroughly incorporating the oil and tallow used for stuffing. The lat- ter is generally done in a wheel heated by steam. The blacking is usually of oil, lampblack, and tallow, with a little tan liquor ; a cheaper black- ing is made of sal soda, lampblack, and soap. Leather finished on the grain or hair side is called grain leather; and imitation grain is made of split leather, which is worked by hand or machine to give its surface the rough look always found on leather finished with the nat- ural appearance on the hair side. Buff leather is where this surface is smoothed off. " Leath-