250 FISHERY INDUSTRIAL PRODUCTS 



ing machine having a revolving emery wheel removes the rough ''bark" 

 from the blank. Rough edges are next smoothed by tumbling the blanks 

 in a churn of water, after which a dryer removes water. The button is 

 then prepared from the blank by an automatic machine. This machine 

 rounds the edges of the blank by means of a sharp steel lathe tool which 

 also turns a depression in the middle of the blank. Then sharp steel drills 

 cut two or four holes. From the finishing machine the buttons go to the 

 polishing room where they are placed for about ll^ hours in revolving 

 barrels containing sulfuric acid, very weak at first but gradually increased 

 somewhat in strength. This process hardens the buttons and prepares 

 them for taking on a high gloss. The acid is removed by steam or water, 

 and the buttons are then given a vigorous shaking in boxes containing 

 sawdust from which they emerge with a beautiful luster. The buttons 

 may be dyed to any shade. 



Products from Skin, Bones, and Sounds 



Leather. The principal deterrent to the use of fish skins as a raw 

 material for leather manufacture is the small size of most fish, which 

 renders the obtaining of large enough skins very difficult. The chief 

 sources of leather from fish, therefore, have been from such large species 

 as sharks. The preparation of furs from seals has already been discussed 

 in the chapter on marine mammals and will not be considered here. 



Because sharks are large enough to obtain a reasonably large ''hide" 

 and since the skin is suitably tough to make a good leather, sharks have 

 been a principal source for leather from fish. Since the disappearance of 

 the natural vitamin A industry from fish livers in the United States, 

 caused by the development of the synthetic vitamin A process, sharks 

 are no longer fished for this purpose in this country, and hence there is 

 no longer a supply of shark skins available as a by-product for leather 

 manufacture. Since, however, there are extensive shark fisheries else- 

 where, a very brief description of general processing methods is included 

 here. 



Suitability of shark skins for leather depends upon the size of the skin 

 and the absence of defects such as scars, butcher cuts, wrinkles, or ex- 

 cessively variable thickness. The skins are carefully removed from the 

 shark either at sea aboard the fishing vessel or as soon as the vessel lands 

 its catch. They are then coated with salt, cured in piles, and shipped in 

 bundles to the tannery. 



The skins are freshened by soaking in water and then treated with 

 slaked lime, after which flesh and other adhering materials are removed 

 by machine. After the usual bating operation to remove lime, the skins 

 are tanned either by the vegetable or chrome tanning process (see Ref, 7 

 for further details). 



