Pearls are special, we’ve known that for millennia, but, unlike gemstones, pearls won’t endure in the same way as their stone companions, unless we know how to wear and care for them properly.
Pearls are an organic gem material, as opposed to a mineral or rock gemstone, and it is this organic nature that determines how we create and enjoy the jewellery they are set in. Pearls are grown by, and inside, molluscs, particularly saltwater oysters and freshwater mussels. When we find a pearl inside a mollusc, it only requires detachment and washing to give us the “finished” gem – pearls do not need to be cut and are soft enough to be drilled through for stringing together – therefore, pearls were one of the earliest gem materials used in jewellery. They have come to symbolise happiness, purity and love – important meanings in Victorian sentimental jewellery – and these meanings, combined with their natural shapes and colours, have made them a key gem for jewellers.
However, molluscs grow pearls only under very strict conditions – they hate water pollution – so it is unsurprising that pearls also require strict care conditions. This guide takes you through everything you need to know about pearls to help you keep your pearl jewellery in its best condition.
The Jewel of the Ocean (and lakes and rivers…)
A world of confusing nomenclature surrounds our pearl purchases: from natural and cultured, to freshwater and saltwater, pearls often come accompanied by a list of descriptors that seem to relate little to the appearance of a pearl, but a lot to its price tag. In reality, all pearls (apart from the increasingly popular, but rare, conch and melo pearls grown by gastropods) are formed through the same process.
Oysters and mussels are the two principal types of molluscs that grow pearls. Different species of oyster and mussel produce pearls of different appearance. Oysters live in saltwater (seas and oceans) and so their pearls are often referred to as marine. Mussels live in freshwater (lakes and rivers).
These molluscs, regardless of type or water, grow pearls by depositing layers of nacre (a mineral substance that builds up to create a harder covering) over an intruding article when their fleshy mantle, which grows the mollusc’s shell, is damaged. In nature, this damage can be caused by disease, attack by other marine life or a parasite. Over time, the mollusc adds layers of nacre, which build up in concentric rings that relate to the mollusc’s seasonal growth patterns, and the pearl becomes larger. These layers of nacre, and the way light interacts with them, give pearls the shiny and iridescent lustre we associate with this gem. Mother of pearl, found on the inside of shells, is a similar layering of nacre.
The term “natural” is applied to pearls that have grown through this process without any interference. Finding natural pearls is, therefore, very rare and their price tags reflect their rarity.
When we initiate this growth process, the resultant pearls are referred to as “cultured”. Cultured pearls are not “fake” or imitations, they have the same characteristic layers of nacre as natural pearls.
We have developed the culturing process in oysters and mussels to such an extent that farms of molluscs produce thousands, if not millions, of pearls every year. For marine cultured pearls grown in oysters, the pearl growth process is stimulated by the grafting of part of the mantle of one oyster into the mantle of another oyster; small mother-of-pearl beads are often introduced at the same time to stimulate the growth of round pearls. Back in the water, the oyster, now with extra mantle and bead, protects itself by wrapping the intruding bead in nacre. The oyster is removed from the water after months or years, depending on the variety and farming practices, and inside should be multiple pearls, reflecting the number of beads inserted.
A similar process is applied to freshwater mussels. We used to find natural freshwater pearls in molluscs living in European rivers, but fishing is now limited. Instead, through the culturing process, many freshwater mussels are used to produce beadless cultured pearls. The same mantle-incision process is applied to the mussels, but no beads are inserted, as the mussel forms a pearl around each piece of inserted mantle. The mussels are returned to lakes for a few years and, when removed, multiple pearls are normally recovered from each mussel. The mussels can be used again for culturing, but the quality of their yield usually declines the more they are used.
The culturing process is closely monitored as water environments affect the growth and condition of the molluscs. Some oyster farms have been granted a protected status that limits the use of boats and other polluting practices in their waters. For farms that uphold sustainable growing and harvesting practices, other marine wildlife benefits from clean and less disturbed water too.
Pearl graders assess a pearl’s colour, shape, size, lustre and surface condition. Pearls, whether natural or cultured, are largely assessed by eye, so you can check on the quality of your own pearls at home. Use a white background so that other colours and shadows aren’t reflected onto the pearls.
A pearl’s body colour is its principal colour, generally white, cream, pink, yellow, grey, brown or black. Pearls often have a pink, green or blue overtone, as well as iridescence. The colours of this iridescence occur when light disperses through the layers of nacre. Iridescence and the reflection of light from the pearl’s surface combine to create the pearl’s lustre. Lustre is generally judged on the sharpness of the reflections.
Some pearls are stained with silver nitrate and exposed to light, which breaks down the solution, leaving a layer of silver below the surface so that the pearl has a permanent grey colour with a metallic lustre. Pale-coloured pearls can be stained different colours to produce pale greens, purples, pinks, reds and yellows. Other pearls are bleached to give them a whiter appearance.
Rounded pearls that have grown away from the shell are known in the trade as cyst pearls. They may be round, oval, pear/drop or button shaped, and their lustre is uninterrupted around their surface. If these pearls have a very uneven shape, they are often referred to as “baroque”.
Pearls that resemble bubbles with a flat back (usually backed with a different material because they have been sawn away from the mollusc’s shell) are known as “blister” pearls.
A pearl’s size is measured in millimetres (mm) across their diameter. For strands of pearls that graduate in size, a millimetre range is given to indicate the smallest pearl’s diameter and the largest pearl’s diameter.
Pearls can have scratches, spots and other marks on their surface. Some of these marks will be natural and some may be due to wear, if set in jewellery. Some pearls grow with ridged surfaces, which can be desirable if a matching pair or set can be accumulated.
Caring for Your Pearls
Pearls’ delicate nature requires a special care routine. Protecting the very thin layers of nacre that make up the lustrous surface of a pearl will ensure that your pearls continue to shine.
Always make pearls the last thing you put on when getting ready. Chemicals, including perfume, sweat and natural residues from our skin, will break down a pearl’s nacre layers. Allow perfume and hairspray to dry before wearing your pearls. Remove pearl jewellery when cleaning or washing up to avoid contact with harsh cleaning products.
After wearing pearl jewellery, wipe the pearls with a clean chamois leather or a soft cloth to limit the build-up of chemicals and natural residue. This cloth could also be useful for wrapping your pearls so that other jewellery in your jewellery box cannot scratch them.
If your pearls are strung as necklaces or bracelets, lie the strands flat in jewellery boxes so that the string does not stretch. Treat your pearls to being restrung (every few years is ideal, but more or less frequently depending on how much you wear them) so that the silk strings are clean and lie properly when worn. Your stringer may also be able to alert you to any issues with your pearls. Contact the Omnēque Concierge for assistance with restringing options.
You can use water to clean your pearls but dry them properly with a soft cloth. Do not put pearls in an ultrasonic cleaner.
Store pearls away from heat sources. Even slight heat can damage pearls, leaving them with cracked or powdery surfaces that detract from their lustre. The orange and pink colours of melo and conch pearls can fade with prolonged exposure to sunlight.
A few of the many names and trade names relating to pearls that you might come across:
Abalone – a large shell (also known as paua shell) with an iridescent rainbow surface made of layers of nacre. Abalone can grow pearls, but they are more commonly cultured to produce the flatter mabé or blister abalone pearls, rather than baroque pearls.
Akoya – marine (saltwater) cultured pearls grown in Japan, usually relatively small and white.
Biwa – the name given to the first cultured, freshwater, beadless pearls because they were grown in Lake Biwa, Japan. The mussel used was native to the lake and produced baroque pearls.
Conch – a gastropod, rather than mollusc, pearl grown by the giant conch. Pink/pinkish-orange and white oval pearls that have a surface appearance closer to that of shells than the lustre of mollusc pearls. They often have a distinctive patterned structure that looks like flames visible through their translucent layers.
Freshwater – baroque pearls from mussels that live in rivers. Cultured in the Mississippi valley in North America and mass-produced in Japan and China.
Keshi – a term first used to describe the small pearls grown by accident, and without a bead nucleus, in the cultured akoya oyster pearl farms in Japan. These small pearls often grow naturally around larger bead-nucleated pearls, but keshi pearls are still considered to be a by-product of the cultivation process. Small Chinese freshwater cultured pearls grown in mussels are sometimes sold as keshi pearls because they have no bead nucleus; however, many members of the trade dispute this characterisation because these pearls are not a by-product, which the term keshi implies, but the intended and cultivated outcome of the mussel pearl growth process.
Mabé – a larger, domed cultured blister pearl, grown from special mabé oysters (Pteria penguin and Pteria sterna) or the oysters that produce South Sea pearls. They are grown using a dome-shaped object that is inserted between the mantle and the shell, and over which layers of nacre grow before the mabé pearl is cut out. These domed pearls are generally set flat in jewellery.
Melo – an orange pearl grown by the Melo marine snail (a gastropod, not mollusc). Melo pearls are often roundish and they have a similar flame-like structure to that of the conch pearl.
Saltwater – pearls that have grown inside oysters that live in seas and oceans.
South Sea – marine (saltwater) cultured pearls, white and golden, larger than Akoya. Grown in waters around Australia, Indonesia and China.
Tahitian – marine (saltwater) cultured pearls, black and grey. Grown by black-lipped oysters in waters around Tahiti and the Cook Islands.
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