In the 21st century, these exquisite organic gems can be worn by women of any status all around the world, thanks to relatively recent methods of growing cultured pearls.

Whatever their value and provenance, pearls are ethereally beautiful minerals that deserve their place in any fine jewellery collection. Here we explore the nature of pearls, and we discuss the differences between natural and cultured, the various types or species, and what to look for when buying pearl jewellery.

What are pearls?

A pearl is a hard, shiny, round mass of calcium carbonate formed inside a mollusc. Not all molluscs make pearls – of the estimated 85,000 living species a mere 20 have the shiny shell needed to produce the same substance in pearl form.

Of these few species, only 1 in 10,000 individuals will ever make a pearl in nature. Naturally occurring pearls are an accident, caused when a small organism or foreign body gets into and embeds inside the mollusc. Over many years this becomes a pearl.

And amongst such rare finds, not all would be an appropriate size and shape for use in jewellery. Molluscs often live on barely accessible floors of seas, rivers or lakes, so alongside their scarcity and magnetising lustrous appearance, this explains why natural pearls are such highly prized and priced gems.

Natural vs. Cultured Pearls

A common misconception is an idea that cultured pearls are fakes or somehow artificial. In reality, you will almost never see a pearl in a jeweller that is not cultured. Here’s why.

Natural pearl stocks were running low at the end of the 19th century as demand for the oysters and mussels and their valuable shells and jewels was extremely high. Luckily about 120 years ago the methods for culturing pearls were discovered that we still use today. The invention of the cultured pearl by the likes of William Saville-Kent and Kokichi Mikimoto made it much easier and economical to produce pearls on a large scale.

A mollusc evolved to produce a pearl as a defence mechanism against foreign bodies or irritants. When the soft inner mantle of a mollusc senses an invading organism it forms kind of blister or sac around the irritant (as it’s called) and traps it within. Then over several years, it deposits very thin layers of shiny, protective nacre around the surface of the sac, which eventually forms into a pearl.

With cultured pearls, a piece of mantle tissue is purposefully inserted into the mollusc to mimic an irritant and kickstart this nacre-building process. This is sufficient for some freshwater pearls. For other freshwater and all seawater pearls, a spherical bead made from mother of pearl must be inserted along with the mantle tissue to encourage the mollusc to produce the nacre lining around it.



Therefore the main physical difference between a natural and cultured pearl is the amount of nacre they are composed of. A natural pearl will be almost entirely made of layers of nacre, and hence can take at least 3-5 years to form a reasonable size. Many cultured pearls, on the other hand, have a thin layer of nacre surrounding a larger, artificially inserted nucleus, meaning they can grow up to size in as little as 18 months.

Cultured pearls are grown in farms in which water conditions, temperatures and feeding can be carefully monitored. Some mollusc species can produce a yield of thousands of pearls in relatively short time scales.  

Nowadays cultured pearls of impressive quality, size and shape can be produced at a fraction of the time of their traditional natural forebears – yet they are still made by the same bottom-feeding marine life.

A cultured pearl is not artificial – it still gets its lustre, colour and value from the nacre deposited by a living oyster or mussel.

Value and use of cultured pearls

Almost all pearls you will find on sale in jewellers these days are cultured. This is due to the tight restrictions on natural pearl diving, and their consequent rarity and extremely high cost. Natural pearls are mostly now sold in auctions as antiques.

Kokichi Mikimoto, a Japanese entrepreneur who first pioneered the cultivation of Akoya pearls, dreamt of “adorning the necks of all women around the world with pearls”. The Mikimoto brand continues to be the foremost producer of cultured pearls. They create fine jewellery pieces distinguished for their combination of timeless elegance and modern design.

At Jacobs, we sell beautiful Mikimoto pearl jewellery, but these aren’t the only type of pearls out there. In fact, they’re a lot more diverse than you might expect.

Types of Pearl

Pearls only form in molluscs which produce a substance called nacre. This is the mother of pearl material which lines an oyster shell. As there are several species which make this iridescent chemical compound of calcium carbonate, we find different kinds of pearls in different molluscs.

These varieties differ in terms of size, quality, colour, shape and value. Here is a rundown of the main types of cultured pearl you’ll see on the jewellery market.

Freshwater Pearls

As the name suggests, these pearls come from mussels which naturally live in freshwater lakes, rivers and ponds. They’re amongst the most common and affordable used in jewellery thanks to their high yield. They tend to be white, peach and pinky purple in colour and come in a range of sizes.

Akoya Pearls

The Japanese original cultured pearl pioneered by Mikimoto in 1893, these are typically small, white, delicate gems. This variety comes from the native saltwater Akoya-gai oyster of Japan which still produces the best quality Akoya pearls in the world.  

Tahitian Pearls

The French Polynesian island of Tahiti is home to a large variety of mollusc which produces pearls of incredible colours of almost any hue – often in combination on the same gemstone. Common tones are peacock, purple and green. These have been the most recently cultivated and are sometimes referred to as “black pearls”.

South Sea Pearls

Silver or golden, depending on the species of oyster that produces them, these pearls are amongst the largest available. They’re remarkable for their size and satin-like lustre. Originating from northwestern Australia, South Sea pearls can be some of the most valuable.

Keshi Pearls

Rather than being defined by the species which produces them, this variety is named for its shape (Keshi being Japanese for irregular shaped ‘poppy seed’). A Keshi pearl has an unusual, non-uniform, pebble-like geometry. It occurs when an oyster ejects the bead it was nucleated with, forming a non-round pearl made entirely of nacre.  

What to look for when buying pearl jewellery

Like all fine jewellery, the quality of any particular precious stone is determined by a few desirable qualities. With the prevalence of cultured pearls, it has become easier to produce a numerous and more consistent product.

However, as they are still forged by living mussels and oysters in an organic process, it’s hard to find two pearls that are exactly alike. A knowledgeable jeweller will be able to talk you through the merits of individual specimens, but it’s worth knowing a little about the basic categories to see for yourself.

1. Size

Big is beautiful. And usually more valuable as well. As with most precious gems, of two otherwise identical pearls, the larger will be worth more. As discussed above, every pearl variety naturally comes in a different spectrum of sizes. However, a good general rule is that the closer you come towards the large end of a species’ dimension range, the rarer it is and therefore the more it will sell for. 

2. Colour

The nature of nacre is that it is layered and refracts light in dazzling ways. This gives a pearl two kinds of colour: body colour and what’s known as overtone – the overall effect of the pearl’s lustre. A third colour effect, known in the industry as orient, refers to the rainbow iridescence seen in mother of pearl.

3. Lustre

The bright, reflective shine of a pearl is what makes it really beautiful to look at, which is why this is possibly the most important quality. Pearls which form in healthy water and in cooler temperatures over a longer period tend to develop deeper, denser layers of nacre. This makes for more reflection and shine from the inner layers and results in a more impressive piece. Lustre is rated Poor, Fair, Good or Excellent by the GIA.

4. Surface

The more perfect the surface of a pearl is, the higher the quality, as far as jewellers are concerned. The fewer blemishes such as bumps, scratches, pits and discolourations the better.

5. Shape

As touched on earlier with Keshi pearls, there is a wide variety of shapes besides the traditional round. A perfect round will fetch a higher asking price than an imperfect spherical specimen (semi or near round). But high-end pearls can also come in button, drop, pear, circled and oval shapes. Baroque refers to an irregular shaped pearl of which Keshi is a variety. 

6. Nacre quality and thickness

The more nacre, the more valuable the pearl. The thickness of the nacre layer is only relevant for pearls nucleated by a bead (freshwater pearls nucleated only by a mantle fragment will grow to be 100% nacre). A thin layer or nacre will affect the lustre and the bead will be more visible. Less nacre also means the gem is more liable to scratching or deformation.

7. Match

Lastly, the overall mix of pearls used on a single piece of jewellery will determine that piece’s worth. Identical pearls on a string will be far more valuable than a mismatched arrangement. This applies to all the above attributes, not just size and colour.

9ct yellow gold 7.5-8mm natural colour freshwater pearl

Black and grey pearl necklace

Mikimoto 18ct white gold 5-5.5mm pearl necklace


Pearls have adorned and been adored by women for centuries. They are one of the most spectacular and breathtaking gems on earth, and a fine piece of pearl jewellery is a thing of exquisite beauty. 

Now that you understand more about these lustrous, organic jewels, talk to a trusted, independent jeweller like Jacobs about the kind and quality of pearl that you’re looking for.

The variety and affordability of these gifts of the sea would not be possible without Mikimoto’s innovations and ideas, and we are proud to stock the Mikimoto brand in our Reading shop.

Give us a call or drop by for a consultation on your requirements and take a piece of the sea with you every day.