540 MARINE PRODUCTS OF COMMERCE 



the vegetable tannin. The chrome solution is freshly prepared by slowly adding 

 a solution of glucose to sodium chromate or by bubbling sulfur dioxide into it 

 tmtil the reduction is complete. The hides are placed in the chromic sulfide solu- 

 tion in a rotating drum for 5 or 6 hours until the tanning operation is completed. 



The chrome process is much more flexible since concentration and time of treat- 

 ment can be varied almost infinitely. This makes it possible to produce a wide 

 variety of leathers, which find many applications. 



Finishing. The skins on being stripped (taken from the boards) are usually 

 given a coat of season, composed of oils or fats, and while in a damp condition 

 are rolled on the jack. When a very bright finish is required, the stock is again 

 seasoned with a mixture containing blood albumen; when this season is bone dry, 

 the skins are subjected to friction on the glazing jack. To bring up the grain so 

 characteristic of sealskin leather the stock is boarded by hand or on the machine. 

 This consists in rolling the skins in such a manner as to produce miniature wrinkles 

 running at different angles along the grain. 



Walrus Skins 



The same procedure as for sealskins is carried out for this class of leather. 

 The resulting product is too heavy for ordinary purposes and must be split to the 

 weight desired. Very few walrus skins are available for commercial leather manu- 

 facture as they are protected by law. 



Sharkskins 



Sharks, like other fish, carry a protective coating; but unlike the hair-bearing 

 creatiires this coating takes the form of scales, or a calcareous deposit known as 

 "shagreen." Before the skins can be utilized for leather, the shagreen, like the hair 

 and epidermis of land animals, must be removed. The earliest method for remov- 

 ing it consisted in scraping the surface with a heavy rasp or file. This operation, 

 as may be well imagined, was time-consuming, very laborious, and exceedingly 

 uneconomical. The leather resulting from this process was not a commercial 

 product and found no ready market on account of its unsatisfactory appearance. 

 A certain amount of raw sharkskin was used for abrasive purposes and for sword 

 hilts; but with the lessening demand for swords and the introduction of cheap 

 abrasives its application for those purposes is a thing of the past. 



The first real advance in the production of sharkskin leather on a commercial 

 scale dates back to 1919 and 1920 when Kohler developed and patented a process 

 for removing the shagreen from vegetable-tanned shark skins. Rogers (1921) 

 developed and patented several processes for removing the shagreen from the 

 raw skin. These patents were assigned to the Ocean Leather Company, which 

 has done more than any other concern to place this industry on a stable basis. 

 In fact the only problem confronting the industry today is that of securing the 

 necessary quantity of skins to meet the ever-increasing demand for the finished 

 leather. Often the hides of sharks are not of sufficiently high quality to be suitable 

 for tanning. Many shark hides show the results of fighting and are deeply scarred. 



Catching. Several methods are employed in shark fishing, one of which con- 

 sists in the use of gill nets. This is more commonly used on the Pacific Coast. 

 These nets are about 300 yards in length and about 12 feet deep. They are 

 anchored across the path known to be followed by food fish; as the meshes are 



