Bleaching
A standard post-harvest treatment that evens out a pearl's colour and lightens it. Near universal in Akoya.
Harvested pearls are often uneven in tone, so they are soaked in a mild bleach under light to bring them to a consistent white.
This is accepted industry practice, disclosed as a matter of course, and it does not weaken good nacre.
Over-bleaching does harm a pearl. It dries the nacre and can leave it chalky, which is why the treatment is a skill rather than a switch.
When you are buying
Bleaching is not something to avoid. It is why a white strand looks matched at all. What matters is nacre thickness underneath, since thin nacre suffers most from any processing.
Maeshori
The Japanese pre-treatment given to pearls after harvest to bring up lustre before they are sold.
Dyed Pearl
A real pearl whose colour has been added after harvest. Standard practice, and entirely fine when it is disclosed.
Nacre
The material a pearl is made of: microscopic aragonite platelets glued in layers by conchiolin. Thickness determines both lustre and lifespan.
Akoya Pearl
The classic small round white saltwater pearl from Japan and China, usually 5mm to 9mm. The pearl in a traditional single-strand necklace.
Matching
How consistently the pearls within one piece agree on size, colour, lustre and shape. A grading factor in its own right.