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<b>Above (L to R) </b>Pacharee; Blue Nile; Mizuki
Above (L to R) Pacharee; Blue Nile; Mizuki

Pearls Part I: Freshwater

Pearls – an organic gem - have been revered pieces of treasure for thousands of years, having adorned the necks of nobility spanning across Persia, Babylon, Egypt, Rome, and beyond.


Image Source: GIA (Top), Mizuki (Bottom)

Before cultured pearls became commercially available at the beginning of the 20th century, all pearl jewellery featured natural pearls formed from wild molluscs. Top quality pearls were highly expensive and mostly reserved for royalty and the exorbitantly wealthy.

When an irritant enters a pearl-producing mollusc, the mollusc enlists a defence mechanism in which it coats the irritant in thousands of microscopic layers of its nacre, which become the pearl.

Cultured pearls are pearls that have grown over a bead nucleus or tissue irritant that humans have intentionally placed into the mollusc. This can be done in various species of mollusc, in both marine and freshwater environments.

Natural freshwater pearls are currently very rare, with most known localities now protected by law.

Throughout history, natural freshwater pearls have been found in most countries all over the world, though the United States was once one of the larger producers. Scotland is another important historical source.

The GIA and other institutions are currently developing techniques for the DNA barcoding of freshwater pearls, to understand them better and identify them.

The culturing of freshwater pearls initially began in Lake Biwa, Japan during the 1920s. It was in the freshwater mussel Hyriopsis schlegeli at Lake Biwa where the successful cultivation of pearls with mantle tissue alone (instead of a bead nucleus) was achieved.

A combination of pollution issues and an improvement in quality of pearls coming from China saw the collapse of the oncebooming production at Lake Biwa. Today, cultured freshwater pearls are largely grown in ponds, lakes, and rivers in China.

Compared with other pearl varieties, freshwater pearls have a particularly large range of sizes, from as little as <3mm, up to pearls of exceptional sizes over 15mm, after multiple graftings.

The size of the cultivated pearl is entirely dependent on how long it is left to grow within the mollusc. For Chinese freshwater pearls, medium sizes around 4–8mm can take anywhere from 2–6 years or so.

Freshwater pearl colours include white, pink, purple, mauve, champagne, orange, lilac, dark blue, brown, and cream. However, most of the cultured freshwater pearls on the market have been treated through various methods to improve or alter their colour – techniques to achieve this include dyeing, bleaching, and irradiation, or combinations of these processes.

Natural freshwater pearls are currently very rare, with most known localities now protected by law.

With a hardness of 2.5, pearl is incredibly easy to scratch - though, still decently durable if cared for. Any initial bleaching treatment, aging, and dehydration can make pearls more fragile.

Always treat pearls delicately – the rule when dressing is pearls are the ‘last on, first off’. This way, damage from everyday chemicals like make-up and perfume can be avoided.

When working with pearls, it is important to avoid all acids, any harsh chemicals, ultrasonics, and steam cleaners. High temperatures may also damage pearls, causing splitting, cracking, or discolouration.

Cleaning with warm soapy water and a soft, clean cloth is always the safest option. For threaded pearls, the silk often used for these strands weakens over time and can collect a build-up of dirt and grime.

If left too long, the strand can snap, and pearls can be lost. Restringing pearls every second year or so (depending on wear) can avoid such instances.

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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 For more information on gems and gemmology ,go to

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