EDITED to add:
Oups... posting in the same time with Jeremy Shephard.
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I am reading the quote a bit differently: to me it says that
"both the quantity (=thickness) and quality of nacre are important, and both are absolutely necessary to have rich lustre on a pearl" Or otherwise saying:
- no pearl with 'thin nacre' can have 'rich lustre'
- not all pearls with 'thick nacre' have 'rich lustre'
- some pearls with 'thick nacre' have 'rich lustre'
- whether 'thick nacre' results in 'rich lustre' or not depends on the
quality of the nacre.
Frankly, I am not sure what exactly all this means as long as there is no clear identification of what 'thin/thick nacre' means and what 'rich lustre' means. Where do the akoya fall? They have thinner nacre than say, south sea pearls and both have thinner nacre than all non-bead nucleated pearls be them natural or tissue nucleated. And yet the lustre of both akoya and south sea is appreciated. Or is that not the 'rich lustre' mentioned in the text?
And so on...
Probably the rest of the book clarifies, but I do not have it.
There has been quite a bit of discussion about the availability of bead nucleated freshwater pearls on this forum. I also was curious about them after finding several accounts and examples scattered around the Net. You may want to run a search for "nucleated freshwater" if not done already. As far as I recall, the conclusion was that:
- round, fine quality nucleated freshwater pearls are/were so few that only count as an oddity,
- that there are continued attempts to priduce nucletaed freshwater pearls that result in low quality, mostly baroque pearls with characteristic 'tails',
- there are serious technical difficulties and economic issues against widespread freshwater pearl nucleation and
- round reshwater pearls resulting from tissue nucleation are already here in mighty fine quality anyway, mostly below 10mm, but with very nice ones up to 13 mm at least.
I think there are accounts of all this on the forum: until now, I have posted every reference I found about this matter here, and Pearl-Guide itself has been a major (make that main) source.
I have not had the heart to purchase round freshwater pearls just for the fun of slicing them up to see if there is a bead inside! And wouldn't... as I suppose that the producers will have no more reason to hide the bead-nucleated status of such pearls than the producers of south-sea and akoya and black saltwater pearls have now (= not much).
My 2c. I am no expert: just trying to offer a shortcut to searching references