Consideration on the Size and Appearance Rate of Natural Pearls: In the Case of Akoya Pearls

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  • 天然真珠の大きさと出現率についての考察─アコヤ真珠の場合
  • 天然真珠の大きさと出現率についての考察 : アコヤ真珠の場合
  • テンネン シンジュ ノ オオキサ ト シュツゲンリツ ニ ツイテ ノ コウサツ : アコヤ シンジュ ノ バアイ

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<p>Cultured pearl technology, completed by the Japanese in the early 20th century, has drastically changed the size and appearance rate of pearls. It is now difficult to know the ecological facts of natural pearls. However, there is a survey report of the Mie Prefectural Fisheries Experimental Stations (Mieken Suisansikenjo) in Japan. In addition, pearl relics, such as the 8th century pearls of the Shosoin Treasure and pearls from Omura Bay during the Edo period, are preserved. They are thought to provide information on the size and appearance rate of natural Akoya pearls. </p><p>Analysis of this survey report and pearl relics shows that the size of natural Akoya pearls started at around 1 mm in diameter, and reached the 10-mm range on rare occasions. The standard size was in the range of 3 to 6-mm. Akoya pearls tended to have a higher appearance rate as they became smaller. This was because some Akoya pearl oysters contained several or dozens of seed pearls. According to the survey report, the number of Akoya seed pearls accounted for 97.5% of all pearls collected, and the appearance rate was 26.62% of the number of collected shells. On the other hand, the appearance rate of large Akoya pearls with a diameter of 4.7 mm or more was 0.015%, which means that 1.5 pieces of pearl appeared from 10,000 shells.</p>

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