Pearl Grading: Lustre, Nacre and What Sellers Won't Say

Pearl grading looks like a scale and behaves like a house style. There is no regulator and no universal AAA. What makes a pearl look expensive is lustre; what keeps it looking that way in ten years is the nacre beneath.

What actually changes what you see

GIA grades pearls through seven value factors rather than letters: size, shape, colour, lustre, surface, nacre quality and matching. Ranked by how much they change what you see, the order differs from how pearls are sold.

Lustre comes first by a wide margin — the sharpness of the reflection, and the one thing that cannot be improved after harvest. Nacre thickness comes second, because it causes the lustre and sets the lifespan. Surface blemishes come third, and matter only if visible at arm’s length. Shape, size and colour mostly move the price. Matching matters on strands, where one dull pearl drags down twenty good ones.

Type	Origin	Typical size	Nacre	Strand price
Akoya	Japan, China	6–9 mm	Thin, over a bead	$250–$800 at 7–7.5 mm
Freshwater	Lakes, China	up to 12–13 mm	Often solid	$120–$400 at 7–8 mm
Tahitian	French Polynesia	8–16 mm	Thick	from about $2,000
South Sea	Australia, Indonesia	8–20 mm	Thickest	$2,000–$8,000 at 10–12 mm

Surface blemishes and the arm’s-length test

Surface quality is the factor buyers over-weight most often. Blemishes that vanish at arm’s length cost little in how the pearl reads; the ones that matter are visible from conversational distance or interrupt the reflection across the dome. Spots, bumps and wrinkles each signal something different. Raised bumps are excess nacre build-up. Wrinkles near the drill hole often indicate a thinner coating at the rim. Discoloured patches can appear where the nacre layers changed during growth.

A strand is judged on its weakest visible member, which is why a single blemished pearl drags the price of the whole row rather than just its own position in it.

Why “AAA” means nothing on its own

It is a trade convention, not a standard: GIA does not grade pearls with letters. Retailers build their own scales, and they do not line up. One publishes A to AAAA across freshwater, Tahitian and South Sea; another uses A to D for Tahitian; Akoya sellers use A to AAA plus a separate Hanadama certificate. Ask what the grade means in that shop: a lustre description, a clean-surface percentage, and a nacre thickness.

The letter system also drifts within a single retailer over time, because the tiers are set by whoever buys the stock. A grade that once meant hand-picked consistency can stretch to cover a broader parcel when supply changes. That is why the useful question is not “what grade is it” but “what does this grade measure here” — and whether the answer survives being written down.

Nacre thickness is the lifespan

A pearl is layers of nacre the mollusk keeps depositing. Bead-nucleated pearls grow that coating over a shell bead; tissue-nucleated freshwater pearls are nacre throughout. Time in the water sets the thickness, which is why the large saltwater types carry more: South Sea nacre is described in millimetres, Akoya in fractions of one. A thin coating looks bright under shop lighting, then dulls or shows the bead. Solid-nacre freshwater pearls cannot peel that way.

Thickness fails from the edges first. The drill hole is the stress point, since the coating is interrupted there and wear concentrates at the rim. A nucleus visible at the drill hole of a supposedly valuable saltwater pearl is a bargaining point, not a cosmetic footnote. Nacre also records its growing conditions: layers of uneven thickness show as faint banding under magnification, the way tree rings do, which is why a cultured pearl is never the flawless sphere counter lighting makes it look.

Matching: where strands are won or lost

Matching is the seventh GIA factor and the only one that operates at strand level. Every pearl in the row has to agree on size gradation, colour tone and lustre before the strand reads as a single object. A strand of individually excellent pearls with mismatched tones looks broken at a glance, while a strand of merely good pearls that match reads as far more expensive than it is. This is also why matched strands price above the sum of loose equivalents: the dealer had to hold back stock until enough similar pearls accumulated.

For a single pendant, matching stops mattering entirely and the pearl is judged on its own factors alone.

How to judge lustre in the room

Step away from the overhead light. Hold the pearl at arm’s length and watch the reflection of a window or phone light on its surface. Judge the edge of that reflection, not its brightness: a sharp, almost mirror-like edge means dense, well-aligned nacre; a soft blur means light scattering before it returns. Check the drill hole too — if you can see the nucleus at the rim, the coating is thin. Then roll the strand and look for one pearl that does not keep up with the rest. A strand is only as good as the chain and clasp holding it, and those metals raise the same base-metal question.

Judge several pearls under one light source and compare them against each other, not against memory. Lustre drifts with lighting: the same pearl that looks flat under one lamp can look sharp under another, and only the comparison within a single light is stable.

Care that keeps nacre alive

Nacre is an organic composite, and it behaves differently from metal or stone. Perfume, hairspray and the acids in skin contact attack the surface, so the sequence that matters is last on, first off: pearls go on after dressing and come off before undressing. A wipe with a soft, dry cloth after wear removes the residue that would otherwise sit on the surface overnight.

Storage has its own rules. Most metals in a jewellery box are harder than nacre and will scratch it on contact, so pearls are kept flat, separate from other pieces, and wrapped in something soft rather than sealed in plastic, which traps moisture against the surface.

Thread is the other clock. Silk stretches and collects skin oils with wear, and a strand eventually needs restringing even when the pearls themselves are unchanged. A knotted strand — one knot between each pearl — loses at most a single pearl if the thread breaks, and the knots keep the beads from grinding against each other, which is why knotting is worth requesting when a strand is restrung.