P. martensii In Pearls
The Japanese have used P. martensii in pearl culture for over a century under the synonym “akoya-gai.” Although several pearl-oyster species are present on the coast of Japan, P. martensii is the only one of importance. Due to the proximity of its habitat to Korea, the species is likely used by Japanese companies in Korean pearl farms as well. This species closely resembles the pearl oyster of Ceylon (originally it was labeled a sub-species of P. vulgaris). P. martensii are distinguished by their coloration: brown and white exterior with an interior lip that is yellow and brown. In contrast, the Ceylon oyster shell has a pink inner lip.
The Pinctada martensii fell from pearl prominance during the Japanese pearl oyster die-off of the mid 1990's. To recoup the industry Japanese imported Pinctada chemnitzii akoya shell from China. The mollusk is now a hybridization of Pinctada martensii and Pinctada chimnitzii. Today, both Japan and China use this shell as the primary akoya pearl producer.
First Use Of The Pinctada Martensii In Perliculture And The Origins Of Discovery
Mass production of P. martensii began in 1890 in Japan. The pearl culturing Industry was centrally located in Ago Bay. The proprietor of the 1,000 acres of sea bottom was the famous Kokichi Mikimoto, who began with about a million oysters and produced a harvest of 30,000-50,000 pearls annually. At this time, (1907), Mikimoto was harvesting only half pearls, that were rarely ever spherical. These pearls were cultured in the shell of the oyster and were deficient in luster, fragile, and only attractive from their upper surface. They could not be used in necklaces.
Dr. T. Nishikawa of the Tokyo Imperial University first discovered the technology to produce spherical “akoya” pearls. In a letter he wrote in 1907, he stated: “It is a great pleasure for me to tell you that I am studying pearl formation and pearl-oyster culture work this summer (1907). Fortunately, I have found the cause of Japanese pearl formation, i.e. the reason why and how the pearl is produced in the tissue of the oyster. I made a practical application of this theory with great prospects for producing the natural and true pearls at will.” (Kunz, George Frederick. The Book of the Pearl. New York: 1908. pp 292-3). The information referenced by Nishikawa in this letter describes the technology that changed the science of pearl culturing from shell nucleation to tissue nucleation. After receiving his patent in 1916, round Japanese akoya entered the pearl market for the first time. It is common misconception that Mikimoto invented this process. Mikimoto acquired Nishikawa's research through marriage to Nishikawa's daughter. Using Nishikawa's process, Mikimoto became famous for inventing round “akoya” pearls from the P. martensii oyster.
It is also important to note that in recent years it has been uncovered that the "discovery" made by Nishikawa was most likely gleaned from a British expatriate living in Australia named William Sawville-Kent who died shortly after discovering the secret of culturing spherical pearls.