Leather: From the Raw Material to the Finished Product

by K. J. Adcock

Fig. 20

SCUDDING KNIFE

Other kinds of hides and skins require additional treatment, according to the class of leather it is intended to make. Hides to be dressed for such purposes as bags, portmanteaus, cases, harness, belting, and stout uppers are usually steeped in an infusion of hen or pigeon dung. A vat is filled with tepid water, a quantity of the dung, usually about half a pailful, is added and well stirred in the water before putting the hides in. The acid fermentation evolved neutralises the lime, while bacteria multiply and rapidly reduce the rubbery limed hide to a soft, flaccid condition. The hides are then well washed in clear water and scudded, after which they are transferred to the tan pits. "Scudding" is the technical name of an operation performed on hides and skins with a special tool, known as the scudding knife, which consists of a convex piece of slate or vulcanite fitted into a wooden or steel handle (Fig. [20]). The hides are placed on the beam, grain side up, and vigorously worked with the knife to scrape off scud (i.e., short hairs, dirt, and soluble lime salts). Both sides of the hides should be scudded for best work. The process of treating hides with excrement is known technically as "bating,"

Calf skins, which are curried or dressed after tanning, should be reduced to a more supple condition than hides intended for harness, belting, and military leathers. A more active dung is, therefore, used for skins of all kinds which have to be rendered supple. Dog manure is generally used, that from the hunting kennels being preferred. Imported dry dung has to be used by some firms, as the supply of fresh dung is insufficient. The demand for the latter is very keen, as it is more effective than the dry product. Goat skins dressed for the famous shoe leather known as glazed or glacé kid, and kid skins for glove leather, need a larger proportion of "puer" than nearly every other kind of leather, for the grain of goat skins is naturally hard and requires a large quantity of dung to reduce it to the necessary softness and suppleness of "kid" leather.

Although these processes can only be described as disagreeable, they apparently have no injurious effect on the workmen. Further, the hides and skins are thoroughly cleaned before putting them in the tan liquors, in which the bacterial activity caused by the infusion of dung is quickly arrested.

Fortunately, from the hygienic point of view, the use of natural "bates" and "puers," although still extensive, is likely to be superseded everywhere by artificial products. So far there are nearly 2,000 tanneries throughout the world where the artificial bating materials are preferred, German and American tanners being the principal users.

The best known artificial bate is "Oropon," which consists of a mixture of pancreatin or trypsin, ammonium salts, and a large quantity of sawdust, the last-named merely acting as a mechanical agent. The enzyme, pancreatin, is the active ingredient, and may be prepared from the intestines of the pig. It has the effect of breaking up the albuminous matters of hides and skins, which are rapidly reduced to a soft and supple condition, while the ammonium salts cleanse them. The quantities used vary according to the degree of suppleness required in the finished leather.

The patentee and vendor of this proprietary article claims that it is suitable for all classes of leather. Hides for sole leather are sometimes treated with a weak "Oropon" liquor in Continental tanneries and, as a result of the cleansing properties of this bating material and its effect in opening up the fibres, the tannage proceeds rapidly. The use of enzymes for bating was discovered by an English leather manufacturer and chemist, who did not take out a patent for his invention, probably because he had previously patented and worked on a commercial scale a bacterial bate which gives very good results but requires much skill in application.

The artificial product, "Oropon," has many advantages over excrements. It is simpler, cleaner, and more rapid in working, and never damages the grain of the skin. On the contrary, great care and experience are needed in using excrements, and the skins may be so badly damaged through negligence as to be almost worthless. Bate burns are fairly frequent when dung is used, and are generally due to hard pieces being insufficiently broken up and diffused in the liquor.