MANUFACTURE OF LEATHER FROM MARINE SOURCES 545 



These measurements are based on the length of the hides, skinned and trimmed. 

 If the extra-long tails are not cut off, deductions are made accordingly. Holes 

 refer to butcher cuts, harpoon holes, fighting scars, etc. 



The foregoing is a general description of how the hides are graded, subject, 

 however, to adjustments according to the length and width of the holes and the 

 size of the sour spots. Generally speaking, if there are only a few cuts, or one or 

 two sour spots on the edges of the hide, these can be trimmed out; but if there 

 are a number of sour spots or holes in the center of the hide, the value is reduced 

 over 50 per cent. 



Ray Skins 



Many species of fish are included under this head (e.g., skates, devilfish, and 

 sawfish ) . Their skins resemble those from sharks in that they carry a layer of 

 shagreen and mvist be handled in a manner quite similar to that described for 

 sharkskins. 



Porpoise Skins 



Porpoise, dolphin, and blackfish— names often applied to the same species of 

 marine mammals— have long been utilized for leather. Their skin is very heavy, 

 and under the dermis there is a thick layer of blubber which must be removed 

 before tanning. This is done in a manner similar to that described under sealskins. 

 Recent investigations, however, have shown that this fatty layer may also be 

 easily separated on the belt-knife splitting machine and the time factor therefore 

 greatly reduced. The blubber, which is separated from the hide proper, is heated 

 in kettles or rendered to obtain its oil content. The skin from the porpoise, as well 

 as from the other species, has on its outer surface a peculiar covering known as 

 the "rubber layer." This layer is readily separated by liming and can be easily 

 removed over the beam or on the dehairing machine. After beaming, the limed 

 skins are bated to remove the excess of lime, and may be tanned either by the 

 vegetable, chrome, or oil process. 



Tanning Processes. In the vegetable tannage of porpoise skins the bated stock 

 is placed in a paddle vat containing a dilute tannin extract. As the union of the 

 tannic acid with the hide substance progresses, more and stronger liquors are 

 required. This strength is obtained by the addition of concentrated extracts to 

 the paddle. The time required for tanning is from 7 to 10 days, and the tanned 

 stock may then be finished in any way desired. In recent years considerable por- 

 poise leather has been made to imitate Cordovan; it produces a very worthy 

 substitute. 



Porpoise Lace Leather. One of the chief uses for porpoise skins in the past, and 

 to a certain extent at present, is in the production of lace leather. This is a very 

 strong material used for lacing machinery belting. The method of producing it 

 involves first tanning the stock, after coming from the bate, with a mixture of 

 alum and salt. To accomplish this the skins are run in a drimi with a mixture 

 of about 5 per cent aluminum sulfate and 5 per cent common salt, to which is 

 added about 0.05 per cent sodium bicarbonate. The skins readily take up this 

 mixture. When penetration is complete, they are hung up and allowed to become 

 bone dry. The longer the skins remain in this dry condition, the better the result- 

 ing leather. After removing from the dry loft the skins are dampened slightly with 



