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Understand the Difference between Natural Black Pearls and Treated Black Pearls


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.

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