Physical properties
The unique luster of pearls depends upon
the reflection, refraction, and diffraction of light from the translucent
layers. The thinner and more numerous the layers in the pearl, the finer the
luster. The iridescence that pearls display is caused by the overlapping of
successive layers, which breaks up light falling on the surface.
In addition, pearls (especially cultured
freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or
black.
Akoya pearl
grafting shed in Xuwen, China.
Freshwater and
saltwater pearls
Freshwater and saltwater pearls may
sometimes look quite similar, but they come from very different sources.
Natural freshwater pearls form in various
species of freshwater mussels, family Unionidae, which live in lakes, rivers,
ponds and other bodies of fresh water. These freshwater pearl mussels occur not
only in hotter climates, but also in colder more temperate areas such as
Scotland: see the freshwater pearl mussel. However, most freshwater cultured
pearls sold today come from China.
Saltwater pearls grow within pearl
oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are
usually cultivated in protected lagoons or volcanic atolls.
Freshwater pearl
mussel |
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