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Gemstones












Above: Yoko London; Tasaki; David Morris
Above: Yoko London; Tasaki; David Morris

Pearls Part III: Akoya

Typically round in shape, white or cream in colour with a pinkish overtone, and possessing a high lustre – Akoya pearls are a classic. For consumers of the western world, these saltwater cultured pearls are the most popular choice.

Unlike the more limited oyster species that produce South Sea or Tahitian pearls, Akoya pearls may grow in any Akoya species complex consisting of

the Pinctada fucata, martensii, radiata,
and imbricata.

These species of oyster are relatively small and generally produce pearls with an average diameter up to 8mm, and much more rarely up to 10mm.
Keshi Akoya – pearls accidentally produced, as a by-product of the cultivation process – can be as small as 0.7mm.

A renowned figure in the pearling world - Kokicki Mikimoto was the first to bring cultured pearls to the market after his experiments with cultivating Akoya pearls via the Nishikawa-Mise method. Mikimoto was established in 1893, followed by the consistent production of pearls circa 1916.

Before these Akoya cultured pearls became commercially significant around the 1920s, pearls were only natural, rare, and very expensive. Cultivating pearls meant new demographics could now enjoy what was once reserved for the elite.

By the 1960s, the pearling industry was an essential contributor to Japan’s economy following World War II. So much so that Japan introduced a prohibition on the culturing of Akoya pearls in foreign countries in an effort to keep the secrets of cultivating pearls within Japan.

Eventually, a combination of factors led to the decline of Akoya pearl production in Japan and a shift, as China became a significant producer of Akoya pearls.

Today, Akoya pearls are still grown in Japan and China, in Vietnam, and since 1999 – right here in Australia.

Unlike the Japanese and Chinese Akoya pearls - known for their thin layers of nacre (0.2mm-0.5mm) and standard bleaching and dye processes to alter colour - Australian Akoya pearls boast a longer cultivation period of 18 months (allowing thicker nacre production) and no treatments post-growth.

Situated on the central coast of New South Wales, the Broken Bay pearl farm climate is ideal for the Akoya pearl species,

Pinctada imbricata fucata. Here, the Australian seeders producing these Akoya pearls are trained in the way of the traditional Japanese method and receive regular visits by Japanese specialists during harvest season.

In addition to their nacre quality, Australian Akoyas come in a variety of colours besides the traditional white. Oranges, greens, dark blues, deep silvers, and light to deep golden hues all naturally occur without treatment.

An on-going challenge in identifying the origin of pearls is particularly prevalent for saltwater pearls in the white to silver hue range, such as Akoyas, as they all form in various Pinctada oyster species.

For a typical gemmologist without access to sophisticated laboratory equipment, examination of the drill hole remains the most useful in separating a bead-nucleated cultured pearl from a natural pearl.

Upon close examination, the drill hole in an Akoya pearl will show a disconformity where the nacre ends, and an organic layer covering the shell bead begins – called the conchiolin.

The layer will often be bleached and dyed, which is a common and accepted practice for Akoya pearls. This visible layer is distinct from a natural pearl's continuous concentric layers of nacre.


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ABOUT THE AUTHOR
Mikaelah Egan

Contributor • GAA Editorial


Mikaelah Egan FGAA Dip DT began her career in the industry at Diamonds of Distinction in 2015. She now balances her role at the Gemmological Association of Australia with studying geology at the University of Queensland. Visit instagram.com/mikaelah.egan For more information on gems and gemmology ,go to www.gem.org.au

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