MANUFACTURE OF LEATHER FROM MARINE SOURCES 543 



ing or glazing jack, or on a brush machine as desired. Either a smooth or shrunken 

 grain may be obtained by adjusting the tannage. The shrunken grain is especially 

 in demand as it produces a very pleasing article when manufactured into bags 

 and cases. 



Chrome Tannage. In the manufacture of chrome-tanned sharkskin leather the 

 shagreen must first be removed, after which the skins are pickled with salt and 

 sulfuric acid and then run in a solution containing basic sulfate of chromium 

 and salt. This operation is usually carried out in a drum, and the test to determine 

 when the stock is tanned depends upon the fact that a chrome-tanned leather 

 will not curl when placed in boiling water. When thoroughly tanned the skins 

 are horsed up overnight to allow the chrome to set, and are then returned to the 

 drum for neutralization. This operation consists of running the skins with a solu- 

 tion of sodium bicarbonate and clear water. The chrome-tanned stock must be 

 shaved to secure an even condition on the flesh side. This is done on a machine 

 which carries a set of spiral knives; as the knife revolves, the skin is placed 

 against the cutting edges. 



Coloring. To color chrome-tanned leather the stock is first run in a solution con- 

 taining tannic acid, for which purpose sumac or quebracho extract is usually 

 employed. This material acts as a mordant for the dyes used to produce the color. 

 The time in the mordant is about Yz hour and about the same time is required for 

 the color. After coloring, the skins are fat-liquored with a sulfonated oil and then 

 hung up to dry. On coming from the dry loft the skins are packed in damp saw- 

 dust to moisten slowly, or as the tanner calls it, "to sammie." When in the proper 

 condition, they are worked on a machine, called a "staker," to soften and stretch 

 them. When well stretched and as soft as desired the stock is tacked out on boards 

 and again allowed to dry. On removal of the dry skins from the boards, or strip- 

 ping, they are given a coat of seasoning and are then rolled or glazed as the 

 demand may dictate. 



Estimating the Value of Shark Hides. Shark hides are bought on measurement 

 (Anon., 1935). The part of the hide over the tail itself and that over the head 

 where the pores are are valueless. These parts are not recorded in the measure- 

 ments nor paid for, so that it is a waste of time to skin them off. The leopard 

 shark and sawshark have two keels or bony ribs, one on each side running from 

 the tail along the body for 4 to 16 inches. This part of the hide of these two sharks 

 is valueless and should be cut off. 



Defects that Reduce Value of Hides. Holes. These may be due to fighting scars, 

 harpoon scars, and butcher cuts. There is nothing that can be done about the 

 fighting scars, but the way to avoid butcher cuts has been described under skin- 

 ning and fleshing. 



Sour Spots. This really means that the hide is rotten in some place. The most 

 frequent causes of sour spots are delay in skinning after death, lack of quick and 

 thorough curing, poor quality salt, or contact with fresh water. 



Burnt Hides. Deep wrinkles in the hides cannot be removed during the tan- 

 ning process, and good marketable leather cannot be produced from hides with 

 deep wrinkles. (Do not confuse these deep wrinkles, produced by faulty handling, 

 with the naturally occurring, shallow wrinkles, always found in the hide of the 

 tiger shark.) Such hides are sometimes called "burnt" hides. Sometimes these 

 deep wrinkles are caused by not laying the hides flat during curing and, as is 



