This document is great snowy day reading...there is also discussion of the use of the term "green amethyst", "yellow emerald" and the like.
Pearl cultivating operations in Lake Biwa Japan began in the 1920’s and enjoyed a boom of production before dying out in the 1980’s due to polluted waters. The introduction of cultured Japanese fresh water pearls in unusual shapes, gave rise to the term “Biwa” which is now commonly used to describe the shape of a pearl.
I also have a couple of strands from Terry Shepherd, in a lovely lavender gray shade. I also had a long colorful pearl ring. I've not had time to reread Strack's chapter on Biwa Pearls. I feel there were plenty of certifiable pearls from Lake Biwa. I seriously doubt even 1% of vendors would be able to name (or care) what kind of mussel their pearls came from.
Wow. So, that means:my little pearls bought in 1980, described as "probably among the last of the Lake Biwa pearls, because of pollution and massive shell die-offs", have no provenance?
and only an old-timer like Fuji Voll, and Sarah Canizarro, who have access to really old stock - and the receipts from the old farmers - those are the only names I remember, have any good provenance. And I remember once, Terry Shepherd.
oh well, disappointing but We buy pearls mostly for beauty, right? When my then husband bought them for me, we didn't know what Lake Biwa meant anyway.