Types of Cultured Pearls

Posted on Sep 29, 2011 in About Pearls

Pearls are an organic gem – meaning that they derive from a living thing – rather like coral and amber and are produced by several types of seawater and freshwater molluscs – mainly oysters and mussels which have a pearly lining on the inside of their shell. There are three types of pearls:

• Natural pearls
• Cultured pearls
• Imitation pearls

Natural pearls

Natural pearls are extremely rare and occur when a grain of sand or parasite enters an oyster's shell and acts as an irritant which the mollusc covers with nacre. Over a period of two years or more a pearl is gradually formed.  It is with natural pearls that we have a rather evocative image of the boy diving into the sea to retrieve an oyster that contains a beautiful single pearl. 

Cultured Pearls

Cultured Seawater Pearls

Cultured seawater pearls result from the insertion of a round bead nucleus into an oyster to stimulate growth of a pearl. The bead is made from the shell of a mollusc found only in the Mississippi River and its tributaries plus a piece of mantle tissue.

There are three main types of cultured seawater pearls

• South Sea pearls
• Tahitian or Black South Sea pearls
• Akoya or Japanese pearls

South Sea Pearls

South Sea pearls are primarily cultivated in the waters of Australia, the Philippines, Burma and Indonesia. The significant colour distinction between South Sea pearls and Tahitian pearls is derived from the oysters in which they are cultured.

South Sea pearls are cultured in the silver or gold-lipped pearl oyster with the natural colour of South Sea pearls usually being white or silver, but they can also come in shades of creamy yellow.

The gold-lipped pearl oyster used to culture these pearls is the world's largest pearl mother and is considered by experts to produce the best pearls in the world. The pearls produced range in size from 10 to 20 millimeters, though pearls larger than 16 millimeters are rare. Their rarity and exceptional size make them highly prized such that they are some of the largest and most expensive pearls available.

Tahitian pearls or Black South Sea

Tahitian pearls or Black South Sea Pearls are cultured in an area of the Pacific Ocean stretching from the Cook Islands eastward through to Tahiti in French Polynesia.

They are grown in the black-lipped pearl oyster and colours produced vary widely from purple, green and black through to shades of grey, cream and even white. The rarest and most highly sought after colour is "peacock green" - the greenish black colour of a peacock feather.

Black Tahitian pearls are generally the same size as White South Sea Pearls ranging in size from 8 to 21 millimeters.

Akoya or Japanese Pearls

Akoya or Japanese Pearls are the best known type of pearl and are cultured from the Akoya oyster with most Akoya pearls being cultivated in China and Japan. The Akoya pearl oyster measures only six to nine centimeters across - less than half the size of Australia's silver-lipped pearl oyster. Accordingly smaller nuclei are implanted so the resulting pearls range from 2 to 10 millimeters in diameter.

Considered the classic amongst cultured pearls and renowned for their perfectly round shape and high lustre, Akoya pearls are produced in white and cream shades with silver or pink overtones.

Cultured Freshwater Pearls

Freshwater Pearls are round, oval or more often than not irregularly shaped pearls that are grown in various species of freshwater mussel.

Typically their size ranges from 2mm to 12mm and their natural colours are pink, bronze, lavender and white.  The only way to find out if a freshwater pearl's colour is natural is by x-ray.  

Increasingly you will find jewellery incorporating multi-coloured freshwater pearls which have been dyed to achieve their striking colours.

Imitation Pearls

A French rosary bead maker developed a coating substance in the 17th century from mixing the sediment of dissolved fish scales with a type of varnish. The subtance is known as pearl essence and is still used to make some of the best imitation pearls in the world such as Majorica pearls. 

Imitation pearls are made from beads of crushed mother of pearl shell, glass, plastic or ceramic material. Sophisticated coating substances and techniques produce imitation pearls which are often difficult to distinguish from natural or cultured pearls. 

Mother of Pearl (MOP) pearls are made from the crushed oyster shell which is then moulded, coated and dyed. They should be treated like real pearls in that they should not come into contact with chemicals and acids, i.e. perfume, hair spray, etc. Sharp objects will scratch the pearls whereas a real pearl is harder to scratch. Additionally, imitation pearls are smooth to touch as opposed to real pearls which are slighlty sandy/grainier.