116 MARINE PRODUCTS OF COMMERCE 



posited arovind the mother-of-pearl bead) is found to be only from one-half to 

 one mm. Thus Japanese cultured pearls have only a veneer of pearl surrounding 

 the core. Furthermore, Japanese sovirces state that it takes from 7 to 9 years 

 to "grow" a cultured pearl. Actually the pearl oyster is capable of depositing one- 

 half mm of nacre in one growing season, or 1 year. In fact the Japanese culturists 



Fig. 7-5. Thin section of a 

 Japanese cultured pearl. Note 

 large mother-of-pearl bead. 



(,Photo by A. E. Alexander) 



often inject various chloride solutions into a pearl oyster to expedite the deposi- 

 tion of calcium carbonate. It thus seems apparent that a cultured pearl takes 

 only a year or two to be produced. 



Japanese cultured pearls are usually yellowish green. The pink color of the 

 cultured pearl, such as seen in a department store, is due entirely to the introduc- 

 tion of a pink or red dye. After the pearls are drilled, the dye solution penetrates 

 the porous microscopic layers existing between the outer nacreous coating and 

 the mother-of-pearl core. Since the coating is only one-half to 1 mm thick, and 

 translucent as well, the dye imparts a pink tint. Any black cultured pearls seen 

 on the market also owe their color to dye. 



There is no easy way to differentiate between a cultured pearl from a natural 

 one. Checking the specific gravity or density is of no avail. Pearls can be fluoro- 

 scoped, radiographed, and subjected to X-ray diffraction methods. The latter 

 techniques are relied on almost entirely. On the basis of the information obtained 

 the pearl expert can quickly and positively distinguish between genuine, cultured, 

 and imitation pearls. 



Pearl Essence and Imitation Pearls 



A Frenchman named Jaquin discovered in 1656 some methods for making 

 imitation pearls. When the silvery material foimd on the surface of many species 

 of fish was applied to beads, it gave them a luster closely resembling that of pearls. 

 At first solid beads were coated with a gelatin solution containing pearl essence. 



