Avi Raz, of A&Z Pearls in Los Angeles, and Dr. Henry Hänni, of SSEF in Basel, Switzerland, have taken issue with the term tissue-activated in pearl culturing (see “Pearl Expert Says CFWCPs Not Tissue Nucleated,” JCK, May 2006, p. 71). “I mean, how strong is the residual activity after the tissue is activated?” asks Hänni, tongue in cheek.
Elisabeth Strack, G.G., FGA, instructor at the Gemmologisches Institut of Hamburg and author of the book Perlen, uses the term tissue-activated to describe the non–bead nucleation process of inserting a piece of mantle tissue into a mussel to create a pearl. Since there is no nucleus, Strack suggests that the inserted tissue activates the mussel’s tissue in creating a new pearl sack.
Grahame Browne writes in GEMS, sixth edition, that the tissue is actually grafted into the tissue of the mussel and therefore should be termed mantle-tissue-grafted. But if the tissue were actually grafted into the tissue of the mussel, there would be no cause for the mussel to create a pearl sack or pearl.
Stimulated might be an alternative to the term activated, but Raz says tissue-nucleated is the proper and traditional terminology.
“By dealing with people from the pearl trade, gemologists, and students, it becomes evident to me that they have, despite their education about pearls, wrong and misleading ideas about how a cultured pearl is formed and how some expressions are meant,” writes Hänni. “There are beadless freshwater pearls from China, which are cultured. They have no nacre thickness as they have no bead. They are not tissue- activated, but, as all cultured pearls, the result of a mantle- tissue transplant, or grafting.
“Earlier, there were bead- nucleated and tissue-nucleated pearls, as GIA likes to say,” Hänni continues. “I am opposed to that. The term nucleation suggests that there is something in the center of the pearl, either a bead or a piece of tissue.” Hänni notes that with tissue nucleation, there is no tissue at the center of the pearl.
In fact, when creating a cultured pearl using a bead, a small piece of mantle tissue is inserted along with the bead. “By the usage of these two expressions, bead-nucleated and tissue-nucleated, it is thus not transmitted that a beaded cultured pearl is also containing a piece of tissue. All cultured pearls are tissue-nucleated.”
Hänni adds, “The tissue grows to create the pearl sack that is producing and containing the cultured pearl. But the term nucleated in relationship with tissue makes people still think that the grafted tissue is in the center of the cultured pearl, in the case of beadless cultured pearls.
“The two terms I would like to read in the CIBJO pearl book instead are grafting (introducing a portion of mantle tissue into an oyster or mussel) and beading (introducing a bead material into an oyster or mussel). There are thus the terms beaded cultured pearls and nonbeaded (beadless) cultured pearls.”