Pearling History

Excerpt taken from my thesis titled "The Effects of Environmental Stressors on Immunological Activity in Pinctada imbricata".

The History of Pearl Production

Fishing for pearls and pearl by-products is an ancient practice. Records from India date back to approximately 4000 B.C. when oysters were harvested for Mother-of-Pearl (MOP). In these times, MOP was acquired for practical uses, namely for the manufacture of buttons, implements, and to a lesser extent, decorations. Natural pearls (keshi) were first discovered as a result of foraging and were subsequently used in cultural and religious ceremonies. In the early 19th century (before the intervention of man) natural pearls were exceptionally rare and obtaining one was costly. This was due to the potential threats to divers which included shark attacks and drowning. It was not until the mid-19th century that wild oyster stocks began to decline, providing an impetus for artificial pearl cultivation.

The history of modern pearl production began with experiments conducted by William Saville-Kent, on P. maxima, in 1890. However, the history of mass pearl production is commonly associated with Kokichi Mikimoto, who successfully produced half pearls (mabe). Shortly after Mikimoto’s discovery, Tokichi Nishikawa and Tatsuhei Mise discovered that by introducing a nucleus and donor mantle tissue (saibo) into the gonad of an oyster, a pearl sac would form around the nucleus resulting in mineralization and nacre deposition. A joint patent was awarded to Nishikawa and Mise. However, a year later, Mikimoto applied for a similar patent, the only difference being his technique included ‘round’ pearl production. This protocol has since dominated the industry and Mikimoto has long been considered its ‘founding father’.

Man-made pearls mimic the natural process of pearl production. An irritant, i.e. nucleus, is inserted into the gonad with a section of saibo tissue. After 7 days a pearl sac forms around the nucleus and at approximately 40 days nacre is deposited. Oysters are typically seeded with a round nucleus.

Modern-day pearls are produced by inserting a nucleus milled from a bivalve shell, typically that of a Mississippi freshwater clam. The nucleus itself is a complex of a protein matrix and an aragonite and calcite crystal structure. The nucleus is coupled with a small 3mm square section of donor mantle tissue (saibo - nacre secreting) and is inserted into the gonad of the recipient (host) oyster. Saibo tissue is selected for and base d on both nacre colour and lustre, as these characteristics are thought to contribute to the resulting pearl. The orientation of the saibo tissue in relation to the nucleus is of significant importance. If the cells that secrete nacre are facing the opposite direction to the nucleus, nacre deposition will not occur. A nacreous layer of aragonite crystals is deposited around 40 days after nucleus insertion at approximately 0-7 layers per day.