Melody, Karin and All,
With my apologies from veering away from the topic of this thread~
When questions about Akoya arise, I always refer to Elizabeth Strack, as I am no akoya expert either. She has compiled 66 pages of fascinating info on these desirable Akoya pearls, so from PEARLS: "Apart from the fact that it influences lustre, nacre thickness is the main determining factor for a pearl's durability. Nacre thickness is a clear indication of the length of time that a pearl spent in the mollusc. Japanese cultured pearls from before World War II had an average nacre thickness of 1 mm. Indeed, a nacre thickness of between 0.6 mm and 1mm was considered normal until into the nineteen seventies. The Mikimoto Research Laboratory in Tokyo has discovered that the nacre thickness must be at least 0.35 mm to produce a good lustre. A thickness of 0.3 mm consists of 5,000 layers of aragonite platelets with a thickness of between 0.35 to 0.5 microns each." (from Pages 376-377)
Other factors affecting longevity are proper care, cleaning, storage, body chemistry of the wearer.
I'm not sure I would say an Akoya pearl would necessarily fade, but they tend to develop a creamier color with age. I don't recall ever hearing 40 years; some Akoya of poor quality certainly would last fewer.
Although not an inexpensive book, I refer to PEARLs frequently, and for anyone purchasing PEARLS, it will no doubt save many times its cost by preventing buying mistakes.
