In
the 13th century, small Buddha-figurines, made of lead,
were fixed to the inner side of clam´s shells in order to have the
figurines coated with nacre.
The first round
pearls were cultivated by the Swedish scientist Carl von Linne in 1761.
In 1893 the Japanese
K. Mikimoto found a way to produce hemispherical pearls, but only the scientific
work of the German F. Alverdes and the Japanese K. Mikimoto and T.
Mise in the twenties made a commercial cultivation possible.
To
start the production of a pearls in an oyster, a round nucleus, turned
out of the shell of an North American mussle, is inserted into the lateral
mantle of an oyster together with a piece of epithelial tissu.
The
inserted epithelial tissue than begins to grow around the nucleus and forms
a pearl-sack. At the inner side of this pearl-sack, thin layers of Aragonite
(Calcium carbonate) and Conchiolin are secreted onto the nucleus and form
the nacre.
These procedure
is used for all salt-water pearls.
Freshwater pearls
without a nucleus are cultivated by only inserting pieces of epithelial
tissue into the mussles. |
Due
to the fact, that a nucleus is not realy necessary a question arises: Why
do we need a nucleus ? The only cause for a nucleus is to increase the
growth-rate of a pearl, because the nacre that surrounds the nucleus is
only a very thin layer. The larger the inserted nucleus, the larger the
pearl !
The
insertion of the nucleus requires skilled hands, which is traditionally
done by femals. Skilled workers can do that up to 300 to 1000 times a day
!
A nucleus of
7 mm has to stay in an oyster for approximately three years, until the
thickness of the layers is 0.8 - 1.2 mm. Nearly 80% of all oysters dye,
if a nucleus of 9 mm and more is inserted, that´s why pearls
are so expensive.
The
oysters are cultivated in bays and live in baskets in 2 - 6 m deep water
, that are hanging down from bamboo-floats.
A few times a
year, the baskets and the oysters are cleaned from seaweed, but also parasites
like fish, crayfish, polypes and certain plankton are bad for the oysters.
Due to the fact, that the temperature of the water has a great influence
on the growth-rate of pearls, and oysters dye below 11 ° C. ,the floats
with the oysters have to be moved into warmer water in winter.
In
the cold Japanese Sea, the growth-rate of nacre is only 0.3 mm per year,
in the South Sea, the nacre grows 1.5 mm per year. |
The
best time to harvest Japanese pearls is the winter, because the production
of nacre stops, which leads to a very good lustre. During the process of
harvesting, the pearls are taken from the oysters, washed, dryed and seperated
into certain groups by colour, size, shape and quality. Only 10 % of the
total production has a very good quality, 10 - 15 % is scrap.
The
first Japanese pearl-farms were founded in Honshu (South Japan), but nowadays
they are located in Shikosku and Kyushu. Since 1956 pearls are also
breed at the coasts of North- and West Australia.
In the 1950´s
a production of freshwater pearls started at Lake Biwa, north of
Honshu. There, 10 rectangular pieces of epithelial tissue are inplanted
at each lateral side of the mussles, in order to grow 20 pearls at once.
Despite the fact, that no nucleus is inserted, the pearls reach a size
of 6 - 8 mm in only two years, but the pearls are seldom round and therefore
inserted a second time to get a bettervshape.
The
natural colours of these pearls are white, rose, orange golden brownish
or blueish, but they are whitened quite often.
The
cultivation is very similar to that of saltwater-pearls, but the mussles
live in only 1-2 m deep water.
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