Pearls are one of the oldest known gem materials as evidence found in early burial grounds used by primitive man has shown. Chinese records of 2000 B.C. mention their use as tribute gifts.
Cultured pearling is attributed to Mikimoto, whom in 1913 marketed the first round cultured pearls to the world market. (Even though 2 other Japanese gentlemen had patented culturing techniques before Mikimoto).
Pearls are made up of 92% Calcium Carbonate (similar to ordinary blackboard chalk) but formed in a different structure therefore much harder.
Pearls are part of the organic group of gems, as are gem materials such as amber, coral, ivory, jet, shell, etc.
Most natural pearls are rare and are found in the Persian Gulf, in the Mannar gulf (between India and Sri-Lanka) and the North West Coast of Australia.
First of all a farm of oysters has to be gathered, and suspended from
rafts in sheltered bays. Once acclimatized they are then ‘seeded' with
a bead made from the shell of the Pigtoe Mussel from the Mississippi River
in the USA.
The oyster, with the aid of some mantle tissue from a donor oyster forms a ‘sac’ around the bead and starts to secret ‘nacre’ in layer upon layer. The pearl farmers need to clean the shells on a regular basis to stop pests such as borer worm and other algae building up on the shell and killing the shellfish inside. Some farms have X-ray equipment to monitor the growth of the pearls inside the oysters.
After about 2–2 ½ years, the oysters are removed from the water for harvesting. If the oysters are in good health they are reseeded for another cultured pearl (generally to grow a larger pearl than the first). If the oyster is in not so good condition they are implanted with a Mabe pearl seed, which is glued to the inside of the shell.
After the pearls are harvested they are then cleaned, graded and sometimes strung ready for sale.
1. South Sea pearls – Grown in the warmer waters around the north West Coast of Australia and other Asian countries such as Indonesia. They are generally larger than their Japanese counterparts, and grow up to 20mm in size, from 8 or 9mm at minimum. Their colouring can be white, silver and cream and some soft pink hues. With gold from Indonesia and Philippines.
2. Black Tahitian pearls – Similar to South Sea pearls as they are grown in the similar sized ‘black lipped oyster’.
3. Akoya pearls – are another name given to Japanese salt water cultured pearls. These pearls range in size from 2mm up to aprox. 10mm
4. Fresh water pearls – are grown in the Fresh water mussel. They are smaller in shell size and can produce multiple pearl culture at the one time, whereas their salt-water cousins can only produce one pearl at the one time. Fresh water pearls take a little longer to grow in the round variety – Aprox. 1-2 yrs for <3mm up to 8-10yrs for >9mm.
1. Cyst pearls - refer to the whole pearls that are cultured from within the shell fish inside an oyster or mussel..
2. Mabe pearls – are the blister or half pearls grown on the inside of an oyster shell. (Both Japanese and South Sea oysters can produce mabe). They are formed by cutting out the mabe then the mother of pearl is removed, the inside bead taken out and replaced with a resin with a backing of mother of pearl glued back on. Various shapes and sizes are available.
3. Keshi pearls – are accidental pearls, formed when a piece of the mantle tissue breaks away from the main sac to form a solid pearl of irregular shape at the same time the first pearl is being formed.
4. Imitation pearls – Pearl beads manufactured by man, to imitate the pearl. Can be made of glass or plastic coated beads.
How do you tell pearls apart?
It is very difficult to tell cultured and natural pearls apart. The only way accepted by a court of law is Xray.
Imitation pearls generally have a very some ‘Plastic’ type finish to them, whereas cultured pearls have a rough ‘gritty’ type texture to them. Also if you look at the string holes, you can see the rough edges where the pearl coating has been put on the bead and dried.
South Sea pearls generally have growth lines around them and are larger than the Japanese pearls.
Some of the new round freshwater pearls are getting difficult to tell apart from the Japanese ones, but they are generally a little more pitted and don’t have as high a lustre on their surface.
Pearls are graded using 5 different categories.
The first of these is the SIZE. The Japanese pearls are grown from around 2½ mm up to 9½ mm. The South Sea pearls grow from 8½ mm up to 20 and sometimes 23mm in size. Mabe pearls range in size from 8mm up to 18mm, and the Fresh water pearls grow from 3mm up to now 9–9 ½ mm.
The second category is LUSTRE. Depending on how healthy
the oysters is and the quality of the surrounding environment i.e. food
in the water etc, depends on how well the nacre is secreted and layered
on the pearl. If the conditions are right the pearl surface is very even
and reflects the light and diffracts some of the light as it penetrates
the surface of the pearl and is diffracted at different angles. So you
see different colours of the rainbow know as the ‘Orient of the pearl’.
The surface, if smooth reflects an almost mirror finish.
So a pearl can be graded as having a high lustre down to a chalky lustre.
The third category is the SURFACE BLEMISHES. Being produced
by nature, the surface of a pearl is not always even and smooth and may
have some pits and bumps on the surface. A pearl can then be graded as
having a clean surface to a heavily pitted surface.
Some pearls are graded using an ‘A’ to ‘D’ grading (A pearls are flawless, B have up to 5 blemishes and 75% of their surface clean, C pearls still have 5 blemishes with 50% of their surface marked, whilst D pearls have more than 50% of their surface marked).
The forth category is the SHAPE. Only about 5% of a pearl harvest come out round or semi round, 70 % of a crop is usually baroque or semi baroque. The gradings are; Round, Semi round, Semi baroque, Baroque, Drop and Circles (circles referring to those South Sea Pearls that exhibit rings around their circumference).
The fifth category is COLOUR. In most pearls there is
a body colour with an overtone colour.
The body colours go in the following order; silver- white, pink-rose, pink, cream and then yellow.
Overtone colours can be green, grey, cream, and yellow.
With the black Tahitian pearls they can be a black, black-rose, black-green, and green-gold down into the blue and blue-grey tones.
A sixth category can come into play when you are looking at strands of pearls and that is the MATCHING quality, all the pearls within a strand must be of similar size, lustre, blemish, shape and colour. Another important criteria when looking at a pearl is the thickness of the nacre. By looking down the string hole you can determine the thickness of the nacre. Sometimes the pearl farmers don’t leave the pearls in the oysters for as long as they should, and as a result the nacre coating isn’t thick enough to with stand a life time of wear and tear and as a result can tend to chip and flake off. Sometimes you can see the mother of pearl bead through the nacre coating.