It's interesting where this thread has lead--especially since it started out with a reference to a natural abalone "free" pearl. Nonetheless, I think that this is a useful and informative discussion that has given me, and probably others as well, much food for thought.
At this point I will timidly weigh in on the subject. Having thought long and hard on the distinctions, (My head is starting to hurt. . . ) I'm inclined to look at them from what I think is more of a "structural" point of view. The object at hand and of value is the Pearl (or concretion) is it not? The mollusc producing it, though of much significance, is not the valued component. Further, it seems that molluscs of both univalves and bivalves produce species that produce nacreous pearls as well as species that produce calcereous concretions. From a functional point of view, the difference in appearance to the eye seems to be one of pearls that are (1) irridescent and can show a play of color that is determined both by
by light refraction, a quality that seems to be enhanced by a rather thinly-layered structure as well as pigmentation and (2) concretions that, though often of great beauty, are not noted for the quality of irridescence. In this case, I would have to say that form or structure is more of a determining factor than source. I lean in the direction of thinking that the only truly important distinction here is one of nacreous vs. calcereous concretions. Perhaps they should simply be considered as the
two separate categories of pearls.
As for the issue of blisters vs. "free" pearls: First I think that one must arrive at an over-riding definition of what the qualities defining a pearl are. My understanding, perhaps mistaken, has been that first, a pearl is an object produced by a mollusc (?--any other contenders of note?) to cover and protect itself from an irritant. Also, as has been noted earlier in this thread, it seems that a pearl must be convex on the whole. Now it seems that a further distinction could be made as to whether the object is attached to and/or a part of a shell. However, my reading on the subject leads me to conclude that both historically and structurally this distinction is not so clear. Some years back I read a lengthy and supposedly authoritative book on the subject of pearls. I think--though am not positive--that it was "The Book of the Pearl" by Kunz and Stevenson. It seems that this book gave at least one, if not more, examples of large and valuable free pearls that presented as blisters. However, by a process of peeling back layers of nacre on the inside of the shell, it was found that under layers of the supposed blister, there was a free pearl that had developed first and then apparently became attached to the shell and covered, resulting in what seemed to be a blister. To further muddy the waters, I have read that the huge and valuable Arco Valley Pearl, which went on sale recently for several million dollars, is suspected to have been attached to the shell when discovered and might well have qualified as a blister. Now where does the distinction between blisters and free pearls leave that one? I find that I am leaning towards specifying blisters as pearls, though perhaps a subcatagory of pearls--especially since reading above that CIBJO is an organization heavily weighted by commercial pearl interests. I am always suspicious of attempts to "self police" when financial considerations are involved. It so often leads to nothing more noble than "He who has the gold makes the rules."
J Marcus
http://www.flyrodjewelry.com/home.html
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