Why do some pearls glow more deeply than others?

The light is doing two things

GIA describes lustre as one of the seven pearl value factors and, for many pearls, the most important. A high-lustre pearl returns reflections that look bright and sharp. A lower-lustre pearl looks hazier or chalkier, even when it is bigger.

Nacre—the material laid down by the mollusc—also influences how light behaves and how durable a cultured pearl may be. GIA’s 2025 update gives greater attention to nacre continuity, rather than treating it as a simple pass-or-fail detail.

A five-minute comparison in a shop

Ask to see two or three pearls of the same type and broadly similar size. Stand near a window or under neutral white light; warm spotlights can flatter almost anything. Roll each pearl slowly and watch the reflected edge of a window, your phone or your own face.

A lively pearl holds a clearer reflection as it moves. Then look for dull patches, a visible bead nucleus, distracting blemishes or weak matching across a strand. Surface marks can be natural and beautiful; the question is whether they disturb the whole piece.

• Compare like with like: akoya with akoya, freshwater with freshwater.
• Judge lustre before size.
• View the piece on skin as well as on a tray.

What the invoice should make clear

Natural, cultured and imitation are not interchangeable words. A responsible seller should identify the product accurately and disclose treatments that materially affect appearance. Ask for pearl type, metal fineness, treatments, return terms and any laboratory report in writing.

A certificate is useful only when you can identify who issued it and what was tested. It does not replace looking carefully. The right pearl is the one whose beauty, description and price agree with one another.