SSEF, the Swiss Gemmological Institute, Basel, Switzerland, examined several chocolate pearls, currently popular, from three producers. The SSEF Laboratory reports that the pearls were dyed, showing “distinct color concentrations” in the very top layers of nacre, below which was seen gray to lighter brown color. SSEF called the under color layer “not darker, as indicated in the propaganda material.”
“This situation relates to simply stained pearls, as it has been commonly done with silver nitrate or today with more modern dyestuffs,” says the SSEF report. The test for silver proved negative on four pearls. “Another coloring agent must be in use,” SSEF writes. “Such a dyeing treatment could also transform white or gray South Seas cultured pearls into chocolate pearls.”
The upshot is that SSEF can’t be certain that all “chocolate pearls” in the trade are “heated Tahitian.” “The fifth pearl in our investigation showed the characteristics of silver staining: Ag [silver] was identified,” the report says.
In the January/March 2007 issue of Pearl World magazine, Bo Torrey writes that Shanghai Gems in Geneva asserts that the chocolate color results from changing the natural melanin within the nacreous layers. While there are several steps to the one-month coloring process, heat was the only process divulged.
Elisabeth Strack, of the Hamburg Gemmological Institute in Germany andpearl expert and author of Pearls, addressed chocolate pearls in her Tucson presentation “Old and New Testing Methods for Pearls.” She reiterated that chocolate pearls are, in fact, treated, and talked about heat, bleach, and “possibly something else, too.”