How is a pearl formed?
When an irritant (e.g. coral, large grit or a bead) enters an oyster/mussel, the mollusc covers the intruder with epithelial cells, forming a pearl sac. These epithelial cells deposit concentric layers of nacre around the intruder, and layer-upon-layer a pearl is formed. Pearls are the result of an oyster/mussel defending itself. If a mollusc does not react in this way it will die.
How many different types of pearls are there?
- The first main distinction is a ‘natural’ and a ‘cultured’ pearl. A natural pearl is formed accidentally, without any human intervention. Natural pearls are very rare and therefore very expensive. A cultured pearl is formed through the human-introduction of an irritant. Cultured pearls are still truly unique as the pearl farmer has no control over what each oyster/mussel will produce (only 5% of a harvest will be of the very best quality). A natural and a cultured pearl look the same from the outside to the untrained eye.
- The second main distinction is a ‘freshwater’ and a ‘saltwater’ pearl. Freshwater pearls grow in mussels living in slow moving rivers and lakes. Saltwater pearls grow in oysters living in protected ocean inlets.
Below are key features in the pearls we have individually chosen to sell.
South Sea Pearls have a mother of pearl bead as the “irritant” and are usually 9-16 mm in diameter. They are produced in white, silver and gold lipped oysters, therefore the natural colours of the pearls are light; ranging from white, silver, pale pink, light gold to a deep orange gold (the colour of the pearl corresponds to the colour of the shell). Found in Australia, New Guinea, the Philippines, Indonesia and Burma. Each Oyster only produces one pearl in its lifetime.
Tahitian Pearls have resin or a mother of pearl bead as the “irritant” and are usually 8-18 mm in diameter. They are produced in black lipped oysters, therefore the natural colours of the pearls are dark; ranging from grey, black, peacock green and aubergine. Occasionally lighter pearls are produced, white, yellow and pink (all with grey overtones). Found in French Polynesia, Panama and Mexico. Each Oyster only produces one to two pearls in its lifetime.
Akoya Pearls have resin or a mother of pearl bead as the “irritant” and are usually 3-10 mm in diameter. Akoya-producing oysters must be at least 3 years old before the “irritant” can be implanted. Natural colours range from pale blue to deep blue, with many blue/grey colours. However, many Akoya pearls are bleached and ‘pinked’, giving them very white through to pale pink and golden tones. They are found in Japan, China, Vietnam, Thailand and Australia. Each Oyster only produces one pearl in its lifetime.
Rainbow Lipped Pearls have a mother of pearl bead as the “irritant” and are usually 8-9mm in diameter. There are only two pearl farms in the Americas, these pearls come from a farm based in the Gulf of California, Mexico. Each technician records his/her name against each pearl during their culturing process, allowing us to track the technician who seeded each pearl, which is truly unique. Their natural colours follow the spectrum of the rainbow. Each Oyster only produces one pearl in its lifetime.
Mabe/Composite Pearls are usually 11-17 mm in diameter. They are grown by attaching a mother-of-pearl half-sphere to a shell. Layers of nacre form on top of the half-sphere, creating a dome. The nacre dome is then cut away from the shell, cleaned and filled with resin and mother-of-pearl. Mabe/composite pearls are used for earrings, brooches or pins.
Baroque Pearls are pearls that are not perfectly round, they have an irregular shape. This irregular shape can range from a minor defect to a distinct oval, curved, pinched, or lumpy shape. They often occur during the pearl production process when organic material decomposes and produces gas. The gas expands between the layers of nacre, forming unusual shapes.
Keishi Pearls are made entirely out of nacre and are almost always irregular in shape. They are formed when:
Either the oyster/mussel rejects the human-introduced irritant, but still produces nacre (creating a small, non-nucleated pearl); or
When a natural pearl occurs in a pearl farm.
Freshwater Pearls are created using freshwater mussels in slow moving rivers and lakes. The size is determined by the amount of time the pearl spends in the water - the longer the time, the bigger the pearl will become. The natural colours are usually white, cream or pastel tones of cream, peach, pink and purple. Natural-freshwater pearls (although very rare) have been found in almost every country. Cultured-freshwater pearls are usually produced in China. A mussel can produce 6-120 pearls. There are two sub-categories of freshwater pearls that are worth noting:
Seed pearls, that can be 2mm or less in diameter; and
Biwa pearls, found in the Sankaku mussel. They originated in Lake Biwa, Japan but are now cultured in China. They are characteristically smooth with a deep lustre
Natural Pearls are made without any human intervention. They usually have rounded surfaces. Natural pearls occur when:
Larva drills through the shell, dies and triggers the pearl producing self-protection mechanism; or
A piece of shell, coral, bone or a large piece of grit attaches to the flesh of the oyster/muscle carrying with it epithelial/nacre producing cells. It is rare that a grain of sand will trigger the self-protection mechanism, these molluscs live in sand and can therefore easily expel it.
In both instances the oyster tries to expel the intruder, if unable the oyster/muscle will start to form a pearl around the foreign body as a form of self-protection. The colours of the pearls can be white, soft pink, mauve, brown and pale grey.