Hey! I will answer as well as I can…
-How long does it take an oyster to turn the inserted bead (or the irritant) into a pearl? That depends on how thick you want the nacre - it also depends on how long you’re willing to risk the oyster (to disease, predators etc.) in the water - the best pearls are cultured for at least around a year and I’m not sure any go over 4 years (in a farming situation).
I would have though the size of the pearl had to do with how long the irritant was inside the oyster and the size of the oyster. Is that at all correct? Yes, although I am not 100# sure about the second part. Pearl farmers always have to try and find the balance between letting the pearls grow for long enough, and not risking their oysters - loss of pysters goes up as time passes.
How does the above question relate to the 1mm nacre discussion? Big pearl, 1mm nacre???
INot sure about this - a very big oyster with a very short-term pearl could conceivably prodice a large pearl with very thin nacre.
- Does harvesting the pearls kill the oyster or can they be used to make more pearls?
No, it kills them. Saltwater pearls, anyway - I think there are some kinds of freshwater pearls that don’t involve killing the mussel.
Did you know that conch pearls exist? They can’t be farmed and are therefore very rare and expensive. My dream is to own one.
Are you considering getting into the hobby? It is expensive and addictive, I am warning you.
EDIT: Here is Jeremy Shepherd (California based pearl expert/seller/guru) in Australia at the famous Paspaley farm with ‘the’ Paspaley pearl (21mm perfectly round South Sea): http://www.flickr.com/photos/pearlparadise/3429693166/ and a closeup of the pearl: http://www.flickr.com/photos/pearlparadise/3428877805/ Paspaley isn’t selling it and I doubt ever will - that quality and size of pearl is so rare that lifetime pearl farmers would generally never expect to see one.