A pearl is the only gem made by a living animal. When something irritates a mollusc’s shell, the animal coats it with nacre — the same mother-of-pearl material that lines its shell — in thousands of microscopic layers.
Natural vs cultured
- Natural pearls form when the intruder is accidental: a parasite, a grain of sand. They are rare to the point of irrelevance in modern jewellery.
- Cultured pearls form the same way, with a deliberate start: a bead nucleus and a piece of mantle tissue are placed in the mollusc, and it does the rest over two to four years. Virtually every pearl sold today is cultured — the process is farming, not imitation.
What makes a good pearl
- Lustre: the sharpness of light reflection off the nacre. The single most important quality.
- Surface: fewer blemishes, higher value — though a flawless pearl is itself suspicious.
- Shape: perfectly round is rarest; baroque (irregular) shapes have their own character and price accordingly.
- Size: driven by the mollusc species and culture time.
Care
Nacre is soft — 2.5 to 4.5 on the Mohs scale. Pearls are last on and first off, wiped with a barely damp cloth after wear, and never stored airtight (they need slight humidity to keep their lustre).