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What are Cultured Pearls? – History, Varieties & Production

  • 12 min read

Cultured Oyster

Cultured pearls are one of the main subgroups of pearls. They come in a vast array of varieties, but also have a rich, deep history spanning over 600 years.

In this comprehensive guide to cultured pearls, we’ll explore that history, the varieties it led to and how exactly pearls are cultured– so let’s begin, what are cultured pearls?

The first signs of culturing

The notion of helping a mollusc create a pearl or a product of beauty has been around since the 14th century. In China, semi-circular pearls or ‘sleeping policemen’-shaped Buddha figurines were made from mud and placed into the interior shell of a freshwater mollusc. The mollusc then obligingly covered the mud figurines in nacre, creating a pearl-like coating.

However, for centuries, these methods weren’t relevant to pearls as we know them, with natural pearls having a long history of their own.

Natural pearls as a symbol of power and wealth

Way back in Roman times, natural pearls were the adornment of choice for those who could afford it. Roman women were so fond of pearls that many husbands were made bankrupt because of an insatiable lust for lustrous pearls.

It’s recorded that Julius Caesar was petitioned to pass a decree ordering that only aristocratic women of the time, also known as ‘Patrician’, could wear pearls. It was passed, meaning ordinary male roman citizens could breathe a sigh of relief.

With no imitating item or substance coming close, pearls reigned supreme. Within Europe, pearls maintained their premium position as the adornment of choice, making them highly prized. It’s no wonder all the portraits of monarchs, male or female, are seen adorned with swathes of pearls. This was basically an attempt to convince any conquering monarch that those portrayed were so wealthy they were beyond defeat.

While portraits of Elizabeth I were no ‘dating card’, their meaning is clear. Don’t mess with me – I am so wealthy that I can afford to sew pearls on my dress. In fact, these ‘pearls’ were iridescent glass beads bought from Venice for one penny a piece – a significant amount of money at the time, and the first relatively convincing imitation pearls.

New discoveries in the East

In 1670, the traveller Tavernier expressed surprise that the Japanese people didn’t hold pearls in high esteem, observing that some fine pearls could be obtained along the coastline of Japan. Half a century later, the Japanese discovered the esteem in which the Chinese held pearls. They were so precious that a pearl was placed in the mouth of the deceased as part of the funeral ritual – ready for a good start in the afterlife.

In 1727, Kaempfer too noted that the finest pearls found were those from the Akoya oyster in Japan, which were not unlike the oysters from the Persian Gulf – reputed to produce the best pearls of all.

Despite these new discoveries, pearls – especially those from a sea oyster – continued to be prohibitively expensive. That was partly down to the love for their gentle glow continuing to grow. It wasn’t long before man decided to give nature a helping hand…

The beginning of cultured pearls

Because natural pearls were so rare and prized, during the XVII and XVIII centuries scientists in France, America and Sweden, tried to help nature. Most notably, the Swedish naturalist Linnaeus, in 1748, studied how to aid pearl formation in a mussel, with muted success.

It wasn’t until 1907 that Tatsuhei Mise & Tokichi Nishikawa discovered, independently and simultaneously, the secret of seeding a nucleus into a living oyster. They each applied to patent aspects central to pearl production. Upon seeing each other’s patent applications, it was clear they had both reached the same conclusion, so they signed the Mise-Nishikawa agreement – which is to this day the heart of pearl culture technology.

The following year, Kokichi Mikimoto applied for a patent to produce full pearls. He had already been granted a patent in 1896 to produce half pearls, or Mabe pearls, which are akin to the nacre-covered ‘sleeping policemen’ half pearls described earlier.

When Mikimoto became aware of the Mise-Nishikawa patented method, he altered his own patent so as not to invalidate it, and bought rights to use the Mise-Nishikawa method. Mikimoto then began an unprecedented expansion of cultured pearls and left Mise and Nishikawa’s names for the history books.

Kokichi Mikimoto’s story

As the founding father of cultured pearls as we know them, it’s worth looking at Kokichi Mikimoto in a bit more detail. Born in 1858, he was the son of noodle and vegetable vendors, and had a dream that every woman should have the opportunity to own a pearl necklace.

An outrageous dream at the time, as a natural pearl necklace cost half a million dollars in the 1900s. But this dream inspired him to change the pearl industry for good. Within a few decades, he had almost achieved his dream – pearls were more accessible than ever before.

At the time of Mikimoto’s death aged 97, a strand of his own brand cultured Akoya pearls was remarkably similar to a natural pearl strand, to the untrained eye. The startling difference coming in their cost – half a million dollars for the natural pearls, versus just a hundred dollars for the cultured counterpart.

When Mikimoto began to produce cultured pearls, they were viewed as ‘fake natural’ pearls. But within a few years, the best jewellers in the world recognised them for their individuality and beauty. At one point, Mikimoto produced 75% of the world’s demand for cultured pearls.

So, what exactly are cultured pearls?

Cultured pearls are produced by human intervention - seeding a nucleus into a living oyster – the Mise-Nishikawa method. Although aided to start their existence, they are completely independent and man has no control over their eventual size, shape, colour or even whether they survive. In other words, each pearl – cultured or natural – is truly individual.

Much like the natural kind, these cultured pearls come in two main varieties – seawater and freshwater. They start life when a technician implants a nucleus and a section of epithelial cells into a pearl-bearing oyster. These oysters are not edible as their effort goes into making exceptional nacre, hence why they produce the most naturally beautiful gem known to mankind.

Pearl production is the reaction of the mollusc in order to protect itself from an alien nucleus – an act of self-preservation. The oyster needs to be three years old in order to withstand the operation, and as an oyster is kept up until the age of seven in the pearl farm, this means there is usually only one pearl produced per oyster.

When the Mise-Nishikawa method of pearl culturing was introduced, they discovered that the best nucleus to use was a round bead made of nacre (mother of pearl) from a freshwater mollusc called a mullette or pig toe. The thick-shelled mussel can be cut into squares, which can then be shaped into round beads of different dimensions. This particular shell was used because it has the perfect specific density to ensure the oyster does not spit it out. Nowadays, however, most nuclei are made from resin.

Unfortunately, not all oysters make the cut. Typically, out of 1,000 oysters that are seeded:

  • 500 (50%) do not make it to pearl production
  • 200 (20%) produce rejected pearls, which are very marked or with large dull patches that look like a dead fish-eye – not something you would want to wear
  • 250 (25%) are pearls of marketable quality
  • 50 (5%) are top quality pearls

This ratio gives the reasoning behind the price calculation of a cultured oyster pearl. The saying “you pay for what you get” has never been truer.

A closer look at the culturing process

The process of culturing an oyster pearl starts with a healthy oyster that’s at least three years old. A peg, similar to an old-fashioned clothes peg, is placed on the oyster so it can’t open. The oyster is placed in front of an experienced technician, who releases the clothes peg and places an obstruction – a bit like a door stopper – at the back of the oyster close to its sexual organ, where there is least resistance.

The technician will make a cut near the sexual organ and place a piece of epithelial cell graft that has come from the mantle tissue of a donor oyster. A round bead is then placed above the epithelial graft, which needs to cover at least a third of the nucleus surface.

If successful it will form a pearl sac which is rather like a placenta. The nervous system of the oyster is very primitive, so the process probably does not hurt much. The implanted oyster is placed back into the sea within minutes. Yet still 50% of the seeded oysters die or eject the nucleus.

A fully functioning pearl sac will secrete layers of nacre onto the bead or nucleus and cover it. The nucleus is enveloped with two layers of nacre produced per tide, and layer by layer, the obstruction eventually forms a pearl. A bit like a foetus in the placenta, the nucleus can turn freely within the pearl sac.

Because these pearls have a nucleus as an irritant, they are termed ‘nucleated’. Cultured oyster pearls are normally harvested in the colder months when the nacre layers are thinner and hence the lustre will usually be at its best.

Generally, each oyster produces only one pearl, which means the oysters are looked after very carefully in a farm. Predators like starfish are kept at bay, with each oyster checked and scrubbed at least three times a year and kept under close supervision.

Where do the oysters come from?

It’s fair to say oysters are a critical part of the pearl culturing process. To make things even more complex, the oysters themselves have a pretty random reproduction cycle. For one, they change sex from one season to another.

The process starts when certain oysters release their eggs or semen into the sea currents, which eventually meet at random. Once inseminated, the egg becomes larvae (fish food) for around a month, before growing into a tiny bivalve shell. At this point, nacre is already growing from the hinge on the inside of the shell, although the shell itself is still relatively gelatinous.

At a month old, the baby oyster will need to find a spot with the right temperature, light and food conditions. Once chosen, it attaches itself with a home brewed “glue” – 90% calcium and 10% protein, tilted upwards, so it can filter its food easily..

Oysters tend to settle in huddles as protection from predators – and once a spot is chosen, the oyster can never move. They open and close using the adductor muscle and feed by filtering what floats in the currents. The oyster continues to grow and the nacre layers get thicker, starting from the hinge outwards. This essentially hardens the shell and makes the oyster less vulnerable.

So how are they actually caught? Originally, and quite effectively, it was done by placing a group of twigs in a suitable spot. With the right temperature and good food through-traffic, baby oysters would settle there before being transported to a farm. The farm provided suitable conditions and protection so oysters could grow until they reached maturity at three years old.

Nowadays, mating takes place in large tanks to avoid complications from the tide sweeping away eggs and semen. This takes place in specialist farms, which grow baby oysters before sending them to other farms for culturing.

Types of cultured pearls

All of the above results in a number of different cultured pearly varieties…

South Sea pearls

Proud, beautiful, large and lustrous are the iconic South Sea pearls, in white, silvery white and gold. They are mainly 9-16mm in diameter, although some can be well over 20mm. Their nucleus is made from a mother of pearl bead or resin, with the nacre covering starting at 1mm and usually 2.5mm or more in thickness.

South Sea pearls are produced in white-lipped, silver-lipped and gold-lipped oysters or Pinctada Maxima. The latter is one of the largest oysters in the world, hence the maxima part of their name. The oyster shell hosts can be as large as 12 inches across, inhabiting the waters of Australia, New Guinea, the Philippines, Indonesia and Burma.

These oysters produce pearls whose nacre is coloured according to the mother of pearl coloration of its host shell. So, white- and silver-lipped oysters birth pearls that are mainly strong white in colour with a range of overtones that range from silver to pale pink and green, or any combination of these. On the other hand, gold-lipped oysters will create pearls that go from a warm creamy white to a deep orange gold hue, running through the gamut of light creamy gold with green and peach overtones.  

Tahitian pearls

Cultured Tahitian pearls resemble luscious multi-coloured orbs. They are mainly 8mm to 18mm in diameter although they can grow to 21mm. The nucleus is a resin or mother of pearl bead and their nacre thickness starts at 0.9mm, and is usually 2.5mm thick or even thicker.

Tahitian pearls grow in the Pinctada Margaritifera. Otherwise called the black-lipped oyster, they produce black pigment and are found in the surrounding area of the archipelago of French Polynesia, Panama and Mexico. Their colours are naturally dark and normally range from grey to black and peacock green to aubergine.

However, they can sometimes be very unusual colours like white with grey overtones, gold, copper, pistachio green, sky blue and pink. There is one clue to spotting if a pearl is created in a black-lipped oyster, and that is their grey overtone.

Akoya pearls

Ranging in size from 3mm to 10mm, and on rare occasions up to 10.5mm in diameter, Akoya pearls start life when a technician implants a spherical resin or mother of pearl nucleus into the pearl bearing oyster, alongside an epithelial cell graft that has come from the mantle tissue of a donor oyster. The graft forms a pearl sac around the resin, or mother of pearl implant, within which layers of nacre are secreted to cover the nucleus.

Akoya pearl-bearing oysters must be three years old before they are able to host a pearl successfully and their life expectancy is only seven years. Mikimoto, who was the first to cultivate pearls extensively, recommended that the irritant should be left in the host oyster for three years. At present the accepted time is 1 ½ years, which results in a good 0.5mm coating. Sadly, economic pressures mean that the irritant is sometimes left in the oyster for only six months, leaving a nacre coat so thin that the pearl blinks when rolled on a flat white surface, allowing us to see the dull mother of pearl bead within.

The nacre of Akoya pearl bearing oysters is naturally found in shades of pale bluish grey, hence the pearls from these oysters are normally born in pale blue, deep blue or pale blue/grey colours. That said, these colours are rarely found for sale. This is due to the fact that for decades Akoya pearls have been bleached and/or pinked by the Japanese to render them  pale in colour. Bear in mind that the first cultured Akoya pearls were considered “fake natural pearls” and had to imitate the colours normally found in natural pearls, which ranged from white with pink overtones to pale gold pearls. Nowadays, cultured Akoya pearls are generally found in all shades of white, from very pure white through pale pink to golden tones.

Cultured freshwater pearls

Cultured freshwater pearls are produced in a mussel as opposed to an oyster. The production of nacre is triggered by the insertion of a piece of mantle tissue that contains epithelial cells from a donor mussel. The graft forms a pearl sac which in turn starts the nacre production.

In general, these pearls have no bead as a nucleus and are therefore termed non-nucleated. When we x-ray a freshwater pearl, it shows solid nacre layers and a very small empty cavity at the centre. This cavity originally held the irritant piece of mantle, which has by now dried up, decomposed and disappeared.

In recent years, some cultured freshwater pearls that have a nucleus have come onto the market – known as potato pearls. To form these almost round freshwater pearls, the farmers have harvested the pearls halfway through their growth term. The harvested pearl is placed in a tumbling machine to render it spherical. This rounded freshwater pearl nucleus is then re-inserted into the mussel, which accepts this pearl bead as its own production and proceeds to coat the rounded pearl with more layers of nacre. The result is almost spherical, very akin to a new potato shape, hence their very unflattering commercial name of ‘potato pearl’.

Freshwater pearls grow under the thick mantle of either side of the shell, and not in the main body of the mussel. Their creation is therefore less intrusive to the creature.

The size of freshwater pearls is purely determined by the amount of time that the pearls spend in the water. The longer they stay in the water, the bigger the pearl will become. The main producer of cultured freshwater pearls is China. It has the technology to produce and improve pearls, and labour costs are very low.

Cultured pearl jewellery

The final step of a cultured pearl’s journey is being used in stunning jewellery, including necklaces, earrings, rings and bracelets. At Coleman Douglas Pearls, we specialise in a selection of beautiful pearl jewellery with a truly personal service.

Working with you to tailor jewellery to match your individual look and style, our expert team will make sure your pearls enhance your natural beauty for years to come.

To find out more, contact us on 0207 373 3369 or email cdp@pearls.co.uk.

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