The lure and lustre of Western Australian pearls

Archeological finds have shown that Paleolithic humans spent time collecting natural objects. Rocks, minerals and organic materials including pearls, shells, bone, coral, amber, ivory and jet were significant to these early humans. These early collections mark the beginnings of jewellery.

Pearls today are some of the most sought-after gems. Some are inexpensive and a few are worth millions of dollars. All have an unwavering allure and are part of a multimillion-dollar industry.

Pearls are cultured in many places including Japan, China, Australia, the Philippines, Indonesia, Burma, Tahiti, the islands of Polynesia and Venezuela.

This story focuses on pearls from Western Australia.

We acknowledge Aboriginal and Torres Strait Islander peoples as the Traditional Custodians of the lands on which we deliver our services. We pay our respects to elders and leaders past, present and emerging.

Aboriginal and Torres Strait Islander peoples should be aware that this story contains images or names of people who have died.

Although pearls can be formed within many species of molluscs, saltwater oysters and freshwater mussels are the most important hosts for marine and freshwater pearls. High-quality lustrous pearls, called nacreous pearls, are of huge commercial importance in the cultured pearl industry.

Pearls are grown when an irritant is accidentally captured inside the oyster shell and nacre forms over the irritant to protect the oyster. A pearl develops by incremental growth of successive layers of aragonite and conchiolin (a protein) around a nucleation site. This material acts as a framework and cement.

All pearls grow seasonally when thin layers of calcium carbonate are added to a nucleus inside the shell. After harvesting, pearls may be used in jewellery with no treatment necessary to reveal their natural beauty.

Due to its combination of warm, shallow water and large tidal movements, the Kimberley region hosts the most conducive environment for the healthy growth of pearls in Western Australia. This is evidenced by the size of the South Sea Pearl (grown off the coast and in bays around the Kimberley).

Optimum water temperature for the fastest growth of pearls is between 23 and 27 °C. Temperatures below 13 °C cause hibernation and for those above 28 °C, the oysters can exhibit exhaustion.

This tidal behaviour increases the activity of marine organisms. These dinner-plate sized oysters can feed on an abundant and constant supply of nutrients, and avoid contamination that might be present in other areas. The waters are pristine in this area north of the State.

Formation of pearls is an example of biomineralization. Many rock-forming minerals crystallize by physical and chemical processes independently of living organisms.

Biomineralization is the process by which the activity of living organisms directly influences the formation of minerals.

It’s the interaction between biology and the environment leading to the formation of structured organic and inorganic composites.

For instance, the decay of marine organisms in seafloor sediment creates an anaerobic local environment in which pyrite (iron sulfide) will precipitate. For pearls, it’s the activity of the live oyster that is key to facilitating precipitation of calcium carbonate around a small, inorganic nucleus inside the shell.

Water is an important component in the chemical processes that generate more than 80% of minerals. Living organisms, such as oysters, produce minerals in a water-based environment, and these minerals can harden biological tissues to form bones, teeth and in this case, pearls.

The following text and images are used with permission of Western Australian Museum: Excerpt from Lustre: Pearling and Australia 2018, edited by Tanya Edwards and Sarah Yu, Welshpool Western Australia, WA Museum, p. 30-39.

Pearling has an illustrious history in Western Australia. Although pearl shell was first reported at Shark Bay by William Dampier in 1699, it was not until the mid-19th century that the resource was actively exploited for commercial gain in Western Australia.

The first recorded operations of the pearling industry in Western Australia were in 1850 when 3 tonnes of pearl shell was shipped from Shark Bay. This early date makes pearling one of the first gem industries in the State.

The Shark Bay pearling industry was centred on Wilya Mia (formerly Wilyah Miah), along an 8 km stretch of the northeastern shore of Useless Inlet. During this time, pearling activities were confined to a bank extending about 16 km north from the mouth of the inlet where pearl shell was bagged and taken ashore for processing.

Pearl oysters most important to the pearling industry in Western Australia are Pteria penguin and four species from the genus Pinctada found in the tropical coastal waters in northern Australia: Pi. maxima, Pi. albina, Pi. imbricata fucata, and Pi. margaritifera.

The shell species collected at Shark Bay were the subspecies Pi. albina, Avicula (meleagrina) fucata, and Pi. cacharium. These shells were smaller and the pearls of lower commercial value than the silver/gold-lipped pearl from oyster Pi. maxima, which lived farther north in the Broome area.

Beginning around 1850, pearl shell was recovered by dredges and pearl diving was phased out.

Following recovery, the landed shell was heated in ‘pogey pots’ until the pearls fell from the shells. As the oyster flesh boiled in these pots and was left to rot, the odour was appalling.

An 1890 report from a pearling camp on Dirk Hartog Island recorded that camps of pearlers were in the area around Notch Point on the eastern side of the island from the early 1870s. Although dredges were cheap and efficient, they destroyed juvenile shells and there were concerns for the environmental sustainability of the industry. As a result, by 1892 pearl shell dredging was banned.

In Shark Bay, shell was taken as a byproduct of pearling from areas where pearls with about a 3 mm diameter were fished.

The town of Denham was the centre of the Shark Bay fishery and employed Aboriginal, Chinese, Japanese, Filipino and Malay workers. Throughout the 1880s many Aboriginal people were forced to dive for pearls and pearl shell in extremely dangerous conditions.

Oysters were collected by hand at low tide or by trawling with metal-framed wire baskets towed by luggers (sailing ships). The catch was shelled, pearls were removed, and the empty shells stacked and dried.

When larger and better quality Pi. maxima shell was discovered farther north, pearl fishing became centred in Nickol Bay in the Karratha area, close to where commercial pearling began. This soon extended eastwards to the area around Cossack (see interactive location map). Here, Pi. maxima shell and pearls were harvested in shallow waters by both Indigenous and non-Indigenous divers.

Pearling continued to spread along the coast and at certain times both Onslow and Cossack became the focus of the industry.

In his book, Pearls and pearling life, published in 1886, Edwin William Streeter gives an account of local history of the pearling industry in Western Australia in the early days. He reported that in the season 1882–83, there were 19 operating vessels, crewed by 539 divers with production valued at £30 300 (equivalent to ~A$7 million in 2022) for shells, and £6000 (equivalent to ~A$1.3 million in 2022) for pearls.

By 1910, Broome had become the world’s largest centre for the pearling industry with nearly 400 pearling luggers and more than 3500 people fishing for pearl shells in the area.

Periculture — production of cultured pearls — was introduced to Australia in 1956 when the pearl farm of Pearls Proprietary Ltd was established at Kuri Bay, 420 km north of Broome.

Some of the world’s most valuable cultured pearls, including the largest, whitest, and most lustrous as well as half-pearls and baroque pearls, are produced in Western Australia.

Broome is now the centre for the cultured pearl industry and Paspaley Pearls has the largest operation. In 2001, black pearl production began at near Dirk Hartog Island at Shark Bay, and at the Houtman Abrolhos Islands 60 km west of Geraldton.

Natural pearls are made by mussels in freshwater rivers and ponds, and by oysters in saltwater, without any human intervention.

Pearls are the product of shells with a nacreous inner shell lining. Nacre is the hard, smooth, iridescent coating on the inner surface of specific mollusc shells, also known as mother-of-pearl. Both the nacre of the shell and that of the pearl are composed of the same material produced by the mollusc’s soft tissue, known as the mantle.

Natural pearls are so rare and difficult to obtain that enterprising people found a way to articially replicate what nature created.

Cultured or farmed pearls form when an artificial irritant is inserted into an oyster shell by human hand, and these need intervention and care. They can be saltwater or freshwater varieties and are still authentic pearls, the best of which command high prices.

To replicate the natural process, cultured pearls are produced by introducing a nucleus and a piece of mantle tissue into the tissues of the pearl oyster. The oyster reacts to this irritation by laying down nacre in the same way it does for the natural process. Cultured pearls can be grown in a marine environment, known as saltwater or marine pearls, or they can be grown in a lake or river system, known as freshwater pearls. Western Australia is well known for its highly prized marine pearls.

Pearls are assessed by growers and sorted into groups based on whether they are unmarked, have one major blemish, or have more than one major blemish. They are then graded for quality using specific criteria.

The large pearls produced by this species are generally 10–20 mm, with the largest recorded diameter being 24 mm. Large cultured pearls of a wide variety of colours produced from Pi. maxima are collectively termed South Sea pearls.

The silver-lipped pearl oyster, also known as the gold-lipped oyster, Pi. maxima, is the largest living species of this genus and grows in a marine environment. It can measure up to 40 cm diameter and has a maximum life span of about 40 years. It is harvested for mother-of-pearl, and produces Australian silver and white pearls.

Black-lipped pearl oysters, Pi. margaritifera, produce pearls in a rainbow of colours that include bronze, grey, black, greens and purples.

The cultured pearl industry produces pearls of various shapes from spherical to irregularly shaped baroque pearls, half-round blister pearls, and irregularly shaped pearl concretions termed keshi pearls. Keshi pearls develop as a byproduct of the cultured pearl process, forming without an artificial bead nucleus. Mabe pearls can be termed blister pearls and are cultured. Blister pearls are found naturally; so naturally occurring blister pearls are not mabe.

Instead, nacre is built up over a section of tissue. These pearls, estimated to constitute at least 15% of Australian pearl exports, look attractive and are desirable for individually designed jewellery.

Pearls develop in many forms, most often spherical, although other irregularly shaped pearls termed baroque pearls can also form. Pearls that are not attached to the shell but develop freely within the host’s tissues are termed cyst pearls.

By contrast, blister pearls develop on the inside of the host’s shell where they form convex bumps on the surface. These blister pearls are then harvested from the shell by sawing.

Mother-of-pearl is the inner layer of the shell in which a pearl grows and has a smooth and iridescent look. The smooth layer appears to be several colours at once and presents a stunning material.

The special lustre of mother-of-pearl is the result of optical effects involving diffraction and interference of light. These optical effects are known as the orient of a pearl and they arise by the accretion of successive layers of microscopic aragonite platelets with optimally aligned crystal structure. Disruption to the orderliness of the structure, or changes to the alignment of crystals, results in a non-nacreous lustre.

In China, records about pearls date back to 2300 BCE and from the 13th century CE, Chinese artisans had discovered the means of coating images with mother-of-pearl. Small artwork made of wood or lead was inserted between the shell and mantle tissue of the Chinese freshwater mussel, Cristaria plicata, so that the surface of the artwork was given a lustrous sheen.

In 2011, a pearl found in Western Australia was estimated to be 2000 years old. Known as the Brremangurey pearl, it is 5.9 mm in diameter and weighs 0.25 g. It was discovered in the Admiralty Gulf area, 80 km east of Kalumburu on Wunambal Gaambera Country, in a midden containing Pi. albina shells about 70 m from the current coastline.

The unusual, natural ‘Southern Cross’ pearl was discovered in 1883. This is an agglomeration of nine natural baroque pearls attached in a cruciform arrangement.

Seven pearls are joined to form a straight stem with the ‘branches’ of the cross formed by two additional pearls.

Its discovery in Baldwin Creek, off the coast between Broome and Derby, was reportedly made by an employee of James WS Kelly, a master pearler.

The Southern Cross pearl was exhibited in London at the Colonial and Indian Exhibition in 1886, and later in 1889 in Paris. This exceptional piece is made up of all natural pearls. It is 37.2 mm long, 18.3 mm wide and weighs 27.3 ct.

The Southern Cross pearl is part of the Western Australia Museum collection.

The pearl industry in Western Australia uses several mollusc species although most production is of large South Sea (cultured) pearls in sites along the northern coastline using Pi. maxima.

Off the west coast of the State, other species used on pearl farms include Pi. margaritifera, the winged oyster Pt. penguin used to produce mabe (blister) pearls, the akoya oyster Pi. fucata martensi for white pearls, and Pi. albina for small yellow pearls.

The industry has been restricted in the State by a quota system for shell collection to prevent overfishing, with some catches below the quota levels because of low demand. Researchers set the quota at a level to ensure that stocks of oysters are sustained over the years. No new licences are being issued.

Cultured pearls grown commercially are produced by the same molluscs that produce natural pearls, although they are developed on implanted, pre-formed nuclei. The culturing process is a surgical procedure that is performed under sterile conditions. It involves grafting a section of mantle tissue (saibo) from a sacrificial or donor oyster together with a pearl nucleus into a recipient oyster.

Despite the care taken in all aspects of the implantation process, mortality rates of host oyster can be high, and other problems including rejection of the nuclei are common. The Australian industry estimates that its mortality rate for seeded shell, over the two-year cultivation period, is about 5%.

Producers expect to seed an oyster four times in its life, the first at about two years old for spherical pearls. It then takes about two years from the time of implantation for a farmed pearl oyster to produce a pearl of commercial value and size. In its last year, the oyster may be used for mabe pearl production.

After collection, shells are cleaned, sized and seeded. Technicians from the pearling companies implant a nucleus and mantle tissue into the shell (seed) from the host pearl shell at the collecting grounds before transporting them to their farm leases.

The seeding process on the fishing grounds uses large vessels holding shells in tanks. The oysters are then allowed to recover for several months from the seeding process in specially designed net panels tied to longlines that sit on the bottom of the seabed in locations known as ‘dumps’.

The seeded oysters are transported to sheltered waters at pearl farms where net panels, on which the oysters mature, are suspended on a floating line from the sea surface. The oysters feed naturally. Within the shell, encystation of the implanted nuclei by the host mantle tissue deposits nacre on the nucleus. This process continues and the oysters are left for about two years.

Pearls cultured using Pi. maxima hosts are harvested after around two years, when the nacre thickness is about 2 mm. Colours include silver, white, yellow to golden, and grey to bluish-grey. The 8–14 mm-diameter nuclei used includes those made from the Mississippian pigtoe mussel. An artificial nucleus, ‘Bironite’, was an experiment and was not generally taken up. Pearl nuclei for the cultured pearl industry are generally made from mother-of-pearl of the freshwater Mississippi mussels.

This product, replacing the increasingly scarce freshwater mussel material, is manufactured from natural dolomite that has been modified by a proprietary process. Bironite is uniformly coloured white, is hard, takes an acceptable polish once converted into a bead, and can be safely drilled with traditional pearl drills.

The Western Australian pearl industry has withstood setbacks including severe weather conditions, changes in shell wildstock quotas, and fluctuations in world demand for cultured pearls. In spite of these factors, it remains the most important aquaculture industry in the State. The environmental impacts of pearl farms are considered negligible and Western Australia is currently the world’s largest producer of white and silver South Sea cultured pearls.

Throughout history, different cultural groups created their own specialized jewellery using whatever materials were available. Although many of the early gem sources are now depleted, new sources have continued to be discovered, as have the jewellery arts and techniques that have evolved to make use of them.

Jewellery was not only created to adorn and beautify its wearer. Early in history, gems attributed all kinds of talismanic powers to the wearer and superstitions abounded. These special powers were thought to confer protection from disease, endow wisdom, prevent drunkenness, or make the wearer invulnerable. No such thing has been proven!

In the 6th century BCE, the Persians introduced pearls into Egypt. Pearls became a desired asset of royalty and have been found buried with the dead.

Pearling had a large impact on the jewellery and associated industries of Western Australia in the late 19th and early 20th centuries. It provided a locally sourced and important raw material to a growing State when it would have been expensive to import other gemstones.

Jewellery items including brooches, pendants, bangles and necklaces using pearls of all shapes and colours, blister pearls and mother-of-pearl, formed the basis of an industry that was unique to Western Australia.

Blister pearls that were considered to have low value formed the basis of this interesting new genre of jewellery. In addition to the pearl fishing aspects of the industry, many different workshop skills evolved from pearling activities including pearl skinning, carving, and piercing work on mother-of-pearl as well as jewellery skills.

The Australian Bureau of Agricultural and Resource Economics and Sciences reports that Australia exported $56 million in pearls in the 2018–19 financial year.

Compare that with exports of $241 million in 2010–11. Between 2019 and 2020, there was a 50% decrease in the trade of pearls worldwide due to the pandemic and geopolitical woes. However, the pearl industry is undeniably resilient and there are predictions that the pearl market will increase by 13% annually over the next few years.

Market tastes might have changed from the desire for that elusive white natural pearl, but there is still huge interest in all shapes, sizes and budget of pearl from mabe, to keshi and other eclectic types of irregular pearls. South Sea pearls will forever retain their market lustre.

While the world’s economy and environmental pressures are changing all kinds of markets, and especially the pearl industry, there is still a huge global market for Western Australian pearls.