Six quality factors, a handful of practical tests, and the questions worth asking any seller.
Lustre is the sharpness and intensity of light reflected from the surface. Hold the pearl under a single light source and look at the reflection. In a high-lustre pearl you can make out a defined image of the light with distinct edges. In a low-lustre pearl the reflection is diffuse and the surface looks chalky. No amount of size compensates for poor lustre.
Pearls grow organically, so minor marks are normal and expected. What you are judging is how visible they are at arm's length. Small blemishes hidden near a drill hole are irrelevant; a prominent pit or crack on the visible face is not.
Round is rarest and priciest. Near-round, oval, drop, button, circled and baroque descend in price but not necessarily in beauty — a well-matched baroque strand can look far more interesting than a mediocre round one, at a fraction of the cost.
Measured in millimetres. Price rises non-linearly: a 9 mm Akoya costs far more than twice a 7 mm, because the larger oysters producing them are much rarer.
Critical for bead-nucleated pearls, chiefly Akoya. Thin nacre means poorer durability and eventual bead visibility. Ask for the figure; good sellers know it.
In a strand, how consistently the pearls agree on size, colour, overtone and lustre. Assembling a well-matched strand takes sorting through thousands of pearls, which is why matching adds so much to price.
| Test | Real pearl | Imitation |
|---|---|---|
| Tooth test | Slightly gritty | Perfectly smooth |
| First touch | Cool, warms slowly | Room temperature |
| Uniformity | Slight natural variation | Identical, machine-perfect |
| Drill hole | Clean, sharp edge | Flaking or chipped coating |
| Weight | Reassuringly dense | Light, especially plastic |
| Rubbing two together | Slight friction | Slide smoothly |
Note that these tests distinguish real from imitation. They do not distinguish natural from cultured — that requires X-ray examination at a laboratory. In practice this rarely matters, because virtually everything on the market is cultured and priced as such.
A knowledgeable seller answers all five without hesitation. Evasiveness on the treatment question in particular is the clearest warning sign in the trade.
Rub the pearl lightly against the biting edge of a front tooth. A real pearl, cultured or natural, has a microscopically layered nacre surface that feels faintly gritty or sandy. An imitation bead coated in lacquer feels completely smooth, like glass. It is crude but remarkably reliable.
For inexpensive freshwater pearls, no. For significant purchases — South Sea, Tahitian, or high-grade Akoya strands — a report from an independent gemmological laboratory confirming pearl type, whether colour is natural, and any treatments is worth having. A seller's own paperwork is not the same thing as independent certification.
No, but price does track a real quality hierarchy. Within a type, lustre matters most, then surface cleanliness, then shape, then size and matching. A smaller pearl with excellent lustre is a better buy than a larger dull one, and usually costs less.