Categories of
Spherical Pearl
Pearls
are the only gem produced biologically rather than through geophysical
processes. Unlike diamonds or other precious stones, pearls does not
require cutting or working to reveal their beauty, because they are
complete in the form in which they emerge from the oysters.
Principally
there are two kinds of pearls, natural pearl and cultured pearl.
`Natural Pearl are the result of misplaced nacre-producing mantle cells.
The only cells that can produce nacre are those of the outermost skin of
the mantle, which lies against the shell. These cells are probably
captured inadvertently by some kind of f
oreign
body (such as a small stone, a piece of shell, grain of sand, or even a
parasite) when penetrating the mantle tissue. The cells are able to
reproduce themselves and surround the intruding object while the nacre
continue to coat it, forming a pearl. Natural pearls are so rare that
thousands of oysters might have to be opened in order to reveal a single
pearl and even then the pearl is likely to be tiny, misshapen and
practically worthless. Cultured Pearls are the fruit of a close
co-operation between their mother oysters, Nature and Man.
Cultured pearls are almost identical to natural ones except that a
person has activated the process by
providing
a bead and a graft tissue to form a pearl. In 1898 the first cultured
pearls were harvested in Japan. But those of the early harvests were not
easy to market. Only between 1916 and 1919 beautifully rounded cultured
pearls became commercially available for the first time. Those were
Akoya cultured pearls. Today, almost all of the pearls sold in the
market are cultured pearls. Here are two main types of cultured pearls,
freshwater cultured pearl and seawater cultured pearl.
Freshwater cultured pearls are cultivated in freshwater molluscs
occurring in places such as the Huazhong region in China (along the bank
of Yangtse ), and Japan’s Lake Biwa. The main producer of freshwater
pearl is China and over 1,000 tons of Chinese freshwater pearls are
coming into the market annually. Freshwater pearls generally have a
lower proportion of organic material in their nacre than pearls from
marine pearl oysters. This gives freshwater pearls a glassy lustre. They
are the cheapest pearls available and look attractive.
Akoya
pearls come from the Akoya pearl oysters ( Pinctada fucata), which are
found in the waters around Japan. They are sometimes called “Japanese
pearls”, but now a large amount of Akoya pearls are being produced in
China as well. The pearl bearing oysters are small and the pearls
cultivated from those oysters are small accordingly. Up until now, they
range from 2mm to 9mm or, very rarely, 10mm in size. The annual
production of Akoya pearls is huge,
around
100 tons each year. The culturing period is short, about 9 months and
nacre coating is much thinner than South Sea pearls. The real advantage
of Akoya pearls is their affordability. A necklace can be purchased for
a few hundred dollar, rather than the many thousand of dollars needed
for a South Sea strand. Japanese tried to produce bigger pearl from
larger oyster, and the first huge pearls were harvested, in 1928, at
Buton in Indonesia. To everyone’s amazement those pearls were 8mm to
10mm in size and had thick nacreous coating. At that time Akoya pearl’s
size range was between 3mm and 4mm.
Above-
mentioned large-sized pearls are called South Sea pearls, which come
from silver-lipped and gold-lipped pearl oyster Pinctada maxima. This
oyster is one of the largest of the thirty or so species of pearl
oysters found throughout the world. Its shell can grow to a diameter of
25cm to 35cm, and it can weigh up to 5kg. The natural habitats of those
big pearl oyster are in warm tropical South Pacific sea waters of the
Arafura Sea off Australia’s north west coast, Indonesia Archipelago,
Philippine Archipelago and Myeik (Mergui) Archipelago of Myanmar. World
War Two obliterated all South Sea Pearl cultivations.
Then in 1957 the sensational South Sea pearls were harvested again in
Myanmar waters. The sizes were from 9mm to 17mm. The South Sea pearl is
a noble pearl and tends to have very strong and healthy nacreous coating
around the implanted mother-of-pearl nucleus. It is this thick coating
that helps keep its natural colour, lustre and beauty, and allows it to
be worn with pride from generation to generation. In 1960s, 1970s and
1980s gem quality Myanmar South Sea pearls were very famous in the
pearling market and buyers from all over the world visited Myanmar Gems,
Jade and Pearl Emporium and bought competitively. Nowadays Australia is
the main producer of South Sea Pearl. Indonesia, Philippine and Myanmar
also produced South Sea Pearl. Annual production of Silver and Gold
south sea pearl is about 5 tons.
Another
kind of large pearl is Black South Sea pearl produced from black-lipped
pearl oyster Pinctada margaritifera whose habitat is the south Pacific.
This oyster is slightly smaller than Pinctada maxima, growing to a
diameter of 12cm to 15cm, with the largest sometimes exceeding 20cm. The
pearls it produces are usually 8mm to 15mm in diameter. The main
cultivation areas are the beautiful islands and atolls surrounding
Tahiti in French Polynesia where cultivation started in the early 1960s.
The first harvest of over 1,000 pearls was in 1965.