German pearl expert Elisabeth Strack, author of the book Perlen, says Chinese freshwater cultured pearls (CFWCPs) are not “nucleated” when mantle tissue is inserted into the oyster. “They are activated,” says Strack. “The inserted mantle tissue is the precursor of the pearl sack in which the pearl grows.” Strack, director of the Gemmological Institute of Hamburg, notes that this scientific fact has been known for several years.

Pearl dealer Marc Freeman has been promoting his PurePearl line of large, round CFWCPs as consisting of 100 percent nacre, and the American Gem Trade Association’s Gemological Testing Center laboratory has recently changed its reports to read that these pearls consist of “approximately 100 percent nacre.”

But GTC still labels these pearls “tissue nucleated.” However, most other laboratories identify them as “mantle- tissue nucleated,” with no comment on nacre thickness.