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Gemstones

Articles from PEARLS - LOOSE / TEMPORARILY STRUNG (34 Articles)











Image courtesy of Brendan McCreesh, O’Neils Affiliated
Image courtesy of Brendan McCreesh, O’Neils Affiliated

The gem detective: identifying pearl

Do you know the difference between freshwater cultured pearls and Japanese akoya? What about natural Tahitians and dyed black freshwaters? Megan Austin takes a closer look.

How does one tell the difference between a natural pearl and its cultured cousin? Any pearl can be X-rayed to reveal its growth structure and confirm a natural or cultured origin; however, this technique is rarely necessary today as the vast majority of pearls are cultured.

There are many pearl imitations on the market including plastic or shell-coated beads, mother-of-pearl beads and even lacquered glass beads that contain ground fish scales called ‘essence d’orient’. Draw the surface of the bead across your teeth – if the surface is smooth, it’s an imitation; if it’s gritty then you have a natural or cultured pearl. The most famous and valuable cultured pearls are marine pearls that originate from oysters of the Pinctada family and include akoya, Tahitian and South Sea varieties. They are prized for their superior nacre – the iridescent outer layer of the pearl – and satiny lustre.

Akoya cultured pearls originate from Pinctada fucata, the same species of oyster used by Kokichi Mikimoto – the Japanese pearl farmer and entrepreneur credited with creating the first cultured pearl.

A spherical bead nucleus inserted into the oyster provides a catalyst around which the nacre grows, forming a pearl. If
a bead nucleus is present when looking down the drill hole, this is confirmation of a cultured origin.

The sizes of cultured akoyas overlap those of freshwater pearls; however, the superior lustre and surface quality of akoyas will separate them.

Tahitian cultured pearls grow around the islands of French Polynesia in ‘black lipped’ oysters called Pinctada margaritifera and display black, grey or brown body colours with various overtones.

South Sea cultured pearls grow between the southern coast of south-east Asia and the northern coast of Australia in Pinctada maxima oysters. The latter may be ‘silver lipped’, resulting in white, cream and silver colours, or ‘gold lipped’ resulting in warm yellow to orange golden tones. The high value of these pearls is linked to a combination of their large sizes, unusual colours and expensive farming costs.

Be on the lookout for treatments that are used to enhance colour. Inexpensive freshwater cultured pearls may be dyed black to imitate Tahitians or dyed gold to simulate South Sea golden pearls. Inspect the exterior surface of the pearl for concentrations of dye, or peer down the drill hole to determine if dyed after drilling. Sometimes lighter-coloured Tahitians may be dyed or the bead nucleus irradiated so the pearl appears black.

Freshwater cultured pearls are predominantly farmed in China using mussels. Freshwater pearls are usually more affordable than marines and available in a wide range of shapes, sizes and colours. Tissue-nucleated freshwaters are mainly baroque with some variations while bead-nucleated pearls are mostly semi-round to round. The difference in lustre and surface quality should set them apart.

Identifying pearl types and treatments can be a complex task. Ask your local qualified gemmologist or NCJV registered valuer for their expertise. 











ABOUT THE AUTHOR
Megan Austin

Megan Austin FGAA FGA Dip DT BA, is a gemmologist and registered valuer. She operates Megan Austin Valuations.
Visit: meganaustinvaluations.com.au.

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Tuesday, 25 February, 2020 06:50am
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