In general terms, the process of currying consists in softening, levelling, and stretching the hides and skins which are required for the upper-leathers of boots and other purposes demanding flexibility and softness, and in saturating or "stuffing" them with fatty matters, not only in order to soften them, but to make them watertight and to give them an attractive appearance.
It is obvious that great differences must be made in the currying process, according to the character of the skin and the purpose for which it is intended, since the preparation of French calf for a light boot, and of the heaviest leather for machine belting, equally lie within the domain of currying. The clearest idea of the general principles involved will be gained by taking a typical case, and afterwards pointing out the different modifications needed for other varieties. The French method of currying waxed calf is selected as an example, since the well-known excellence of this leather makes it interesting to compare the details with the methods ordinarily in use in this country.
After raising the skins from the pits and beating off the loose tan, they are hung in the sheds till partially dry, great care being taken that the drying is uniform over the whole skin. In modern shops, this drying is usually accomplished at once, and in a very satisfactory manner, by means of a hydraulic press. If dried in the air, they must be laid in pile for a short time to equalize the moisture, and then brushed over on flesh and grain. The next process consists in paring off loose flesh and inequalities. This is done on a beam, and with a knife similar to that used in bate-shaving. This knife has the edge turned by rub-ting with a strong steel, and is called couteau a revere.
Next follows the mise an vent The skins are first placed in a tub with water or weak tan-liquor for 24 hours; they are then folded and placed in a tub with enough water to cover them, and beaten with wooden pestles for 1/4 hour. At the present day, stocks, or a " drum tumbler," a machine on the principle of the barrel-churn, usually take the place of this hand labour. The skin is next placed on a marble table, flesh upwards, and with one flank hanging somewhat over the edge, and is worked with a "sleeker " or stretching iron. The first two strokes are given down and up the back, to make the skin adhere to the table, and it is then worked out regularly all round the side on the table, so as to stretch and level it. The flesh is then washed over with a grass-brush, the skin is turned, and the other flank is treated in the same way. It is lastly folded in four, and steeped again in water. The next process is the cleansing of the grain. The skin is spread again on the table as before, but grain upwards, and is worked over with a stone set in handles, and ground to a very obtuse edge.
This scours out the bloom; after washing the grain with the grass-brush, it is followed by the sleeking-iron as on the flesh.
The next step is re-setting. For this, except in summer, the skins must be dried again, either by press or in the shed. This is another setting out with the sleeker, and, the skin being dried, it now retains the smoothness and extension which are thus given to it. The skins are now ready for oiling in the grain, for which whale-oil or cod-liver oil is generally employed. (Olive-oil, castor-oil, and even linseed-oil, may, however, be used, and are sometimes made into an emulsion with neutral soap and water.) After oiling the grain, the skins are folded, and allowed to lie for two or three days before oiling the flesh. The oiling on the flesh is done with a mixture of degras and tallow, in such proportions as not to run off during the drying. Dejras is the surplus oil from the chamois-leather manufacture, which in France is effected by daily stocking the skins with oil, and hanging in the air for oxidation. The degras is obtained, not by washing the skins in an alkaline lye, as in the English and German method, but by simple pressing or wringing. This oil, altered by oxidation, is so valuable for currying purposes that skins are frequently worked simply for its production, being oiled and squeezed again and again till not a rag is left.
It is generally mixed in commerce with more or less of ordinary fish-oil. Eitner recommends, where the degras is of indifferent quality, a mixture of 65 parts degras, 20 of neutral soap (i.e. soap without the usual excess of alkali), and 15 of soft tallow. After oiling the flesh, which is accomplished by extending the skin on the marble table with the sleeker, and applying grease with a sheep-skin pad, it is hung to dry at a temperature of 65° to 70° F. (18° to 21° C). After drying, the surplus oil is removed by a fine sleeker from both flesh and grain, and the skins are ready for " whitening." This consists in taking a thin shaving off the flesh, and was originally accomplished by the shaving-knife on the currier's beam; some curriers are still in favour of this method. It is now, however, done by a sleeker with a turned edge. The grain then undergoes a final stoning and sleeking, to remove the last traces of adhering oil, and the skin is grained by rubbing it in a peculiar way under a pommel covered with cork.
It is then coated on the flesh with a mixture, of which the following is a specimen: - 5 parts of lampblack are rubbed with 4 of linseed-oil, and 35 fish-oil are added; 15 of tallow and 3 of wax are melted together and added to the mixture; and- after cooling, 3 of treacle. This compound is put on with a brush, and allowed to dry for some days. Finally, the skins are sized over with a glue-size, which is sometimes darkened by the addition of aniline black.
The hide to be curried is placed upon a table, and a warm iron is rubbed over the flesh side; it is then turned over, and the grain side is moistened with water and rubbed with a copper sleeker until it is nearly dry, after which the colouring matter, made of Brazil-wood and yellow berries, is applied to the grain, and it is once more rubbed with the sleeker; it is then spread out to dry, and the final finish is given by rubbing the grain with a glass sleeker. This produces a very fine grade of leather for riding bridles, russet reins, etc. Use a strong solution of soda, apply it to the freshly-cut edges, and when nearly dry, rub with a woollen rag until a good polish is produced. To finish the edges of russet reins, use salts of tartar and water. If discoloured, first remove the stain with a weak solution of oxalic acid.