We have hitherto alluded chiefly to the preparation of the thick hides used for sole leather, among which several varieties may be found, each distinguished by a different technical name, by which its thickness, quality, or mode of preparation is known; but the thinnest and weakest hides, as well as the skins of calves and other animals, are also prepared for use as upper leathers, in which case it is necessary to reduce their thickness by _shaving_ or _paring_ them down upon the flesh or inner side, before they are subjected to the action of the tanning infusions. Such hides or skins also require, after leaving the hands of the Tanner, to be rubbed, softened, and dressed by the currier, in order to bring them to the necessary degree of flexibility and smoothness. The currier also has recourse to shaving or paring with a peculiarly formed _knife_, to bring the skin to the requisite tenuity; and it is his office to blacken the surface, which, for common shoe leather, is done on the flesh side, although for some purposes leather is blackened on the outer or grain side. Horse-hides, which are comparatively weak and thin, are sometimes dressed in the latter way, under the name of Cordovan hides, from the circumstance of such leather having been formerly made at Cordova, in Spain. Calf-skins supply the quality of leather most generally preferred for the upper part of boots and shoes. Of the thin skins prepared for ornamental purposes, many are tanned with a substance called _sumach_, prepared from a plant of the same name. The tanning is performed by sewing up each skin into the form of a bag, with the grain or hair side outwards, and nearly filling it with a strong solution of _sumach_ in water. The bag is then fully distended by blowing into it, and the aperture is tied up; after which it is thrown into a large shallow vessel filled with hot water containing a little sumach. The distended bags float in this vessel, and are occasionally moved about with a wooden instrument until the solution which they contain has thoroughly penetrated their substance. Owing to the thinness of the skins and the heat to which they are exposed, this operation is performed in a few hours. The process is expedited by taking the bags out of the solution, and piling them upon a perforated bench or rack at the side of the tub, so that their own weight may force the confined liquid through the pores. [Illustration: Apron. Gloves. Whetter. Roller. Leoline.] When the tanning is completed, the bags are opened to remove the sediment of the sumach; the skins are washed, rubbed on a board, and dried; after which they are ready for dyeing and finishing with a ridged instrument, which imparts to the surface that peculiar grain by which morocco leather is distinguished. An inferior kind of leather, known as “imitation morocco,” is prepared in a similar manner from sheepskins. [Illustration: Plungers. Tongs. Jet. Hook.]