Fig. 57.
In the case of strap-butts, the currying is, of course, far less elaborate. They are well scoured out, heavily stuffed, and stretched in screw-frames, to prevent their giving afterwards when in use.
In Germany, Switzerland, and Austria, a method of stuffing strap-butts is frequently employed, which, so far as I am aware, is not in use in England. It is called Einbrennen or "burning in," and consists in applying very hot tallow to the dry leather. The butts are washed free from liquor in a tumbler, boarded to soften them thoroughly, scoured, set out with a sleeker, nailed on laths, and air-dried. They are then very completely dried in a room heated to 104°-113° F. (40°-45° C.), as if any moisture remains in the hide, the fibre will be destroyed by the heat of the melted tallow. The tallowing generally takes place in the same room, as a high temperature is required to allow it to soak in, and the leather would greedily reabsorb moisture if exposed to damp air. The tallow is heated, generally by steam in a jacketed pan, to 167°-212° F. (75°-100° C.). There are two ways of applying it. The melted tallow may be applied on a table to the flesh side of the butt with a ladle, and rubbed on with a brush or rag. In this case, as soon as the tallow has sufficiently soaked in, the butts are placed in water to prevent its striking through to the grain. The second way is to have the pan of sufficient size and suitable shape, and for two men to draw the butt through the melted tallow with tongs, and more or less rapidly according to the quantity it is desired that the leather should absorb; and in some cases the process is repeated once or more. In this case, it is useless to wet in water, and the butts are allowed to cool gradually in pile.
The leather is now impregnated with grease, but it is far from being properly stuffed. Instead of the grease being spread over the finest fibres in a minute state of division, it simply fills the spaces between the larger fibres. To remedy this, the butts are well softened in water (which, if they have been drawn through the tallow and allowed to cool, must be tepid), and are then worked in a damp condition in a drum tumbler, by which they brighten in colour and become uniformly stuffed. They are then allowed to lie in a pile a day or two, are stoned and worked out with the sleeker, and hung up to dry. When in right temper they receive a final setting out with the sleeker, and when dry are either rolled or glassed. For further details, Nos. 256 and 257 of 'Der Gerber,' 1885, must be consulted, where the matter has been exhaustively treated by Eitner, in his papers on "Extract-Gerberei."
Fig. 58.
In England, curried leathers are generally sold by weight, which leads to the use of glucose and other materials to add to the weight. In America, all upper leathers are sold by measure, and this is now ascertained by a very ingenious machine ([Fig. 58]). The skin is laid on a latticed table, and a frame, from which rows of bullets are suspended, is let down upon it. The total weight of the frame is indicated by a spring balance, and as the bullets which are over the skin are supported by it, the diminution of weight indicates the measurement. Several modified forms of this machine are now made.