Leather: From the Raw Material to the Finished Product

by K. J. Adcock

FLUFFING MACHINE

The chrome sole leather used for ordinary boots is quite a different product, and it is only in the last two or three years that it has been used to any extent. The "Dri-ped" is the best known make of this leather. The tannage is effected by the one or two-bath methods already described. The processes preparatory to chroming are very important, as it is essential to get the maximum yield of pelt. The hides are, therefore, often treated with sulphide of sodium, which loosens the hair in twenty-four hours or less. They are then placed in fairly strong limes for two or three days to swell the fibres and saponify the grease. After being washed in cold water, the hides are treated with a weak solution of lactic, boracic, or butyric acid, or butyrate of ammonia, to remove all trace of lime, when they are ready to be chrome-tanned. After chroming them, neutralisation of the acid chrome salts is effected with borax, and the leather is ready for dressing. The principal objects of this process are to make the leather firm and waterproof, and to remedy its tendency to slip easily on wet pavements. The last-named is the greatest difficulty, and there are only about two or three firms who have really surmounted it. Each manufacturer keeps his recipe secret, but the ingredients that go to make the various dressings are drawn from the following: Stearines, mineral oil, Tragasol, resin, carnauba wax, beeswax, paraffin wax, glue. Resin, or asphalt, or both, may be used to prevent the leather slipping in contact with a wet pavement. One patent describes a method of dressing chrome sole leather with a mixture of asphalt, resin, and paraffin wax.

Fig. 34

STRIKING-OUT AND SCOURING MACHINE

The waterproofing ingredients are preferably applied to the leather in the tumbler at a high temperature, say, 160-170° F. After running the drum for about three-quarters of an hour, the leather is impregnated with the mixture, and is then horsed up for at least twenty-four hours to allow complete incorporation of the fatty ingredients with the fibres of the leather. A suitable waterproof dressing and filling increases the strength of the leather.

The finishing of the leather is simple. The butts or bends are smoothed and stretched out by machine (Fig. [34]), oiled on the grain, nailed or extended with special metal grips on square wooden frames, and dried. In some cases, they are hung up until nearly dry, rolled by machine instead of being put on boards and aired off in a drying stove.

A patented method of making waterproof chrome sole leather to prevent it slipping and losing its shape in wear consists in first treating the leather in a solution of glue, gelatine, agar-agar, or other colloidal substance, with the addition of formaldehyde, and then submitting it to strong pressure under the influence of a high temperature, in order to fix the colloidal matters. The pressure is made between heated plates. The leather is afterwards impregnated with a mixture of wool-grease, pitch, asphalt, resin, wax, gutta-percha, etc. A recipe given in the specification consists of wool grease (60 parts), asphalt (10 parts), soft pitch (25 parts) and gutta-percha (5 parts). The mass is fused and kept at 90° C. The hides are placed flat in this mixture, which they quickly absorb.

If the British Government should ever introduce a Bill to stop the adulteration of leather, it may be found somewhat difficult to deal with chrome sole, which must have some filling material to make its use practicable. No exception can be taken to the dressing of leather with materials that make it waterproof and increase its strength; in fact, much more will be done in this direction than has ever been attempted in the past, as waterproof sole leather is a necessity in Great Britain. Any measure to check the adulteration of leather must, therefore, clearly define the chemicals which are known to be harmful in leather and which may not be used. This has not been overlooked by the Australian Government, which has forbidden the use of barium salts in leather, and likewise the importation of leather boots or any goods made of leather containing this chemical. Such goods sent to Australia are liable to confiscation, and it is reported that a few consignments of boots have already been condemned.