CHAPTER 8 



Mother-of-Pearl and Blister Pearls 

 Mother-of-Pearl 



Introduction 



Mother-of-pearl is widely used for decorative purposes. It is impossible to 

 estimate accurately the world's annual production of pearl objects, but it is 

 probably in the neighborhood of $100,000,000. The marine pearl-shell fisheries 

 are located principally in Australia, the Netherlands Indies, the Philippine Re- 

 public, Japan, the Persian Gulf, the French Pacific Islands, India, and New 

 Zealand. Manufacture of pearl buttons is centered in the United States, England, 

 France, and Japan. Italy and France use large quantities of pearl shells for the 

 manufacture of jewelry and ornaments. 



Practically the only marine mother-of-pearl shells produced in the United States 

 are those taken in the abalone fishery of southern California and in the scallop 

 fishery of the Atlantic Coast. However, thousands of tons of fresh-water clams, 

 taken from the Mississippi River and its tributaries, are used to make pearl buttons 

 and other useful ornaments. 



According to the U. S. Department of Commerce the United States imports 

 of unmanufactured mother-of-pearl shell in 1948 totaled 5,288,718 pounds, 

 valued at $2,513,727. Australia was the leading supplier of these shells, sending 

 1,422,603 pounds, valued at $1,005,925. The Netherlands Indies supplied 1,181,- 

 932 pounds, valued at $570,363; the Philippine Republic, 935,334 pounds, valued 

 at $388,826; the French Pacific Islands, 529,525 pounds, valued at $188,980; 

 and New Zealand, 264,113 pounds, valued at $94,103. Smaller quantities came 

 from some 15 or more additional areas. United States imports of mother-of-pearl 

 manufactures (including shells and mother-of-pearl engraved, cut, ornamented 

 or manufactured) amounted to $13,808, principally from Italy and France. 



Great Britain carries on a considerable traflSc in shells, which is especially 

 important in the commerce and industry of many of the outlying divisions of the 

 Empire. Australia is the largest contributor to the British shell market. 



Structure and Composition 



The shell of the pearl oyster is formed of three main layers, the outermost 

 designated as the periostracum. Within this is the "prismatic layer", which is 

 thicker than the outermost layer and constituted by an aggregation of calcareous 

 columns or prisms disposed at right angles to the periostracum. In this, as in other 

 parts of the shell, there is a combination of organic and inorganic substances. The 

 organic part, termed conchiolin, is a nitrogenous substance similar to keratin, 

 forming a kind of network for the deposition of carbonate of lime. Within both of 



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