A Tahitian pearl's value comes down to seven factors: lustre, size, surface cleanliness, shape, colour and overtone, nacre thickness, and how well pearls match across a strand. Lustre matters most — a sharp, mirror-like glow lifts a pearl above everything else — followed by size and a clean surface. Learn these and you can compare any two pearls honestly.

Price talk around pearls gets murky fast, partly on purpose. Strip away the labels and only a handful of things actually move the number. We grade against these every day at the bench, so here's the plain version, ranked the way we'd rank it.

The seven factors, ranked

Why lustre beats everything

Lustre is light bouncing off the layered nacre laid down by the oyster Pinctada margaritifera. A pearl with deep nacre and a tight crystal structure throws back a crisp, almost mirror-sharp reflection — hold it near a window and you can nearly read the room in it. A dull pearl, however large, never excites the eye the same way. If you remember one thing from this guide, judge lustre first and let the rest follow.

Colour is natural, and that matters

A Tahitian's body colour ranges from pale dove grey to near-black, and a fine Tahitian layers on overtones of peacock, green, blue and aubergine that drift as it turns. These colours are grown by the oyster and are never dyed, which is exactly why a naturally vivid example commands a premium — the lagoon produced it, not a tint bath. Flat, even, "too perfect" colour across a cheap strand is usually the tell of treatment.

How grading scales fit in

Most sellers summarise surface and lustre on a producer scale — AAA, AA, A — set by farms and dealers. It's useful shorthand, but it's a trade scale, not a GIA grade, so always ask what a given seller means by each tier. GIA assesses pearls on its own separate seven-factor system. And to be clear, we never frame a pearl as a financial vehicle; buy the pearl you love at a fair price, for the pleasure of wearing it.

Getting the most pearl for your budget

• Trade a millimetre of size for noticeably sharper lustre — it reads richer on the neck.
• Accept a clean drop or baroque shape instead of perfect round to stretch the budget.
• Let a couple of tiny surface marks save you money; they vanish at arm's length.
• Buy loose and build a strand over time if a fully matched necklace is out of reach today.

Are bigger pearls always more expensive?

Usually, since size is genuinely rarer at the top of the range, but not always. A smaller Tahitian (Pinctada margaritifera) with superb lustre can easily outprice a larger, duller one. Glow wins.

Is a round pearl worth the premium?

Round is the rarest shape, so it carries a premium — but a clean drop or an interesting baroque can be just as beautiful for noticeably less. Shape is where personal taste can save you money.

Compare lustre and colour for yourself across our loose Tahitian pearls, and if you want to be sure a pearl is the real thing first, read how to tell if a Tahitian pearl is real.