After the stoving is complete, the product is given a few days under ordinary atmospheric conditions to permit the reabsorption of moisture to the usual extent. Enamelled leathers are then grained to develop the pattern. REFERENCE. Bennett, "Manufacture of Leather," p. 380. PART III.--CHROME LEATHER SECTION I.--THE NATURE OF CHROME LEATHERS In these days the manufacture of chrome leather has attained a position hardly less in importance than that occupied by the ancient method of tanning by means of the vegetable tanning materials, and large quantities of hides and skins are now "chrome tanned" after preparatory processes analogous to those described in connection with vegetable tannages (Part II., Section II.; and Part II., Section I.). Chrome leathers are made by tanning pelts with the salts of chromium, and are typical of what are known as "mineral tannages," in which inorganic salts are the tanning agents. Tannage with alum and salt (see Part IV., Section I.) is one of the earliest mineral tannages, but is now of relatively minor importance. Chrome tanning was first investigated by Knapp (1858), who experimented with chromic chloride made "basic" by adding alkali, but his conclusions were unfavourable to the process. A patent was taken out later by Cavallin in which skins were to be tanned by treating with potassium dichromate and then with ferrous sulphate which reduced the former to chromic salts, being itself converted into ferric salt. The product, which was a combination of iron-chrome tannage, did not yield a satisfactory commercial leather. Another patent, taken out in 1879 by Heinzerling, specified the use of potassium dichromate and alum. This in effect was a combination chrome-alumina tannage. The alum had its own tanning action and the dichromate was reduced to chromic salts by the organic matter of the skin itself and by the greases employed in dressing. The process, however, was not a commercial success. In 1881 patents were obtained by Eitner, an Austrian, whose process was a combination chrome and fat tannage. The chrome was employed as "basic chromium sulphate" made by adding common soda to a solution of chrome alum until a salt corresponding to the formula Cr(OH)SO{4} was obtained. Such a solution is now known to be perfectly satisfactory, but at first it proved difficult to devise satisfactory finishing processes, and to supplement the chrome tannage with the fat tannage.