General color of pearls jewelry do not have to change color, but if see black ash, black pearls, attention should be on the alert for its rare, as may be stained. As far as is known, pearls add to silver nitrate soaked in the solution, removed after the sun drying on strong, that is, become black.
The difference between them is: natural black pearl strand is not pure black, but slightly rainbow-like flash of deep blue black, or a bronze color with the black pearl stained uniform color, luster poor, black and black ash, such as cloth dip 1:05% solution of dilute nitric acid scrub Pearl, a black cloth on the track. Three common knowledge in distinguish between imitation pearls: Filling wax imitation glass beads in a circular hollow milky white glass ball in a paraffin. This imitation-density, generally lower than 1.5 Cg/3cm, OK to hand to difference. Needle-detection by the internal sense of a soft, outer-carved fixed, smooth surface. Imitation solid glass beads will be milky white glass ball solid immersion in the "pearl in the semen" from. 15 times magnifying glass used in the drilling observation, only see an extremely thin "pearl semen," and finished jewelry the loss but not the small scale-like powderi. Plastic coating in the milky white plastic imitation-plated beads, a thin, "pearl semen" and using a magnifying glass observation of the surface coating evenly distributed papules-than natural pearls as cultured pearls or paste is formed. With needle provoke, falling into a film, no small powder. In addition to eye over counterfeiting, the identification of other characteristics are not dissolved in hydrochloric acid. In polarized light microscopy showed heterogeneity, and natural pearls in polarized light microscopy significant heterogeneity. As China's booming market for pearls, pearl jewelry to the people demand more and more. On the market, especially on the coastal resort , the phenominon of pearl products of cultured pearl strands, pearl imitation posing as natural pearls, harmed consumers , so the correct appreciation of pearls is very necessary.