A natural pearl
of any color, shape and size is very expensive. Unlike cultured pearls, they
are not produced under tight controlled conditions but form naturally when an
irritant like sand grain gets stuck within the body of the oyster.
The sand grain
irritates the animal and to ease its discomfort starts to coat the grain with the
coating of calcium carbonate or nacre. This nacre buildup hardens to form the
shiny and lustrous pearl. The lines inside the shells of the oyster is luminous
and iridescent, this is the same substance that pearl gets made up off.
How black pearls get formed?
Natural black pearls
The color,
shape, and size of the pearls get influenced by the oyster type it gets
produced in. Black pearls get formed when sand grain penetrates in the black
lipped oyster called Pinctada Margaritifera. Interior shell of basically every
oysters are glossy silver or white but the Pinctada Margaritifera oyster
features thick black band, so if pearl forms close to this band it absorbs the
coloring.
The extremely black
pearl jewelry you see indicates that the pearls got produced very close
to the oyster’s lips. If they get wedged in lighter section then they get
silvery gray color. In case an oyster produces white pearls but has strange
black color in its nacre then it too can produce blackish pearls. This is a
rare occurrence, especially one in ten thousand pearls.
Treated black pearls
White pearls are
dyed or irradiated to gain the black color.
·
Irradiation method
Gamma ray’s irradiation darkens the saltwater pearls’
nucleus leaving nacre alone thus the pearl gains a blue or gray color. Same
treatment is done with freshwater pearls and dark colored pearls are obtained.
Radiation does not get retained but irradiation treatment improves the orient,
so it is safe to wear the jewelry.
·
Dyeing method
Another method used to dye is French dyeing. Silver
nitrate chemically reacts with the white colored nacre causing it to turn
black.
Both methods are
not permanent treatment because overtime the colors can fade. Natural black
pearls differ a lot from treated ones. In a strand, if all the black pearls are
well-matched consistently then they are possibly treated. You can see a
darkened nucleus inside the drill hole, which indicates irradiation treatment.
Color concentration also is visible in the pearl dyeing treatment.
