SOLE-LEATHER.—Treatment in the Shed. Fig. 44. The butts, after being treated as above described, are frequently oiled lightly on the grain, and are taken into the drying-lofts, where they are hung on poles till about half dry. They are then laid on the floor in piles, and covered up till they heat or "sweat" a little, which facilitates the succeeding operation of "striking." This is performed by laying the butt over a horizontal "beam" or "horse," and scraping its surface with a triangular pin, shown at D in Fig. 25. This pin has an even, though tolerably sharp, edge, and is so used that it stretches and smooths out the grain, without breaking it; and at the same time Fig. 45. Fig. 46. Butts are now generally struck by the very ingenious machine of Wilson, whose name has also been mentioned in connection with the disintegrator, and which is shown in Fig. 45. The arms carry blunt brass or steel knives or sleekers, and work outwards from the centre, while the butt is carried backwards and forwards over the drum. Stones may be substituted for the sleekers, when it is required to remove the bloom. The machine requires a firm foundation, as its reciprocating motion causes considerable vibration. Fig. 47. After a light oiling and a little further drying, the butt is laid on a flat "bed" of wood or zinc, and is rolled with a brass roller loaded with heavy weights. Various machines are also in use for this purpose. In Fig. 46, is shown Wilson's spring butt-roller, in which the pressure is produced by Fig. 48. The leather is now frequently coloured on the grain with a mixture, for which each tanner has a recipe of his own, but usually consisting mainly of yellow ochre with size or It is very important, and especially so with heavy mixed tannages, that the drying should be conducted in the dark, and not too rapidly. No artificial heat should be used, except in frosty weather, to wet leather; and it should be carefully protected from harsh drying winds. After the leather is finished, it should be dried off in a well-ventilated drying-shed, heated to about 70° F. (21° C.). The same observations apply to the drying of rough dressing-leather, except that artificial heat should be avoided. Frost makes dressing-leather porous, and prevents it carrying a proper quantity of grease in currying. On the construction of drying-sheds, see pp. 243-54. |