Natural Round Diamonds

The round brilliant is the shape the entire diamond market is priced against, which is exactly why a natural round is the easiest stone to buy well and the easiest to overpay for. Supply here is deeper than in any other shape, so two stones with the same weight and the same letters on the report can sit a long way apart on price — and the difference is almost always cut.

Cut is the one grade we would not compromise on in this shape. A round brilliant has 57 facets arranged to return light straight back at the viewer; when the proportions drift, the stone goes flat in exactly the lighting where you will actually see it. An Excellent cut in a lower colour will out-perform a mediocre cut two colour grades higher, every time.

Two levers save real money on mined rounds. Buy just under the round weights: a 0.92ct faces up the same as a 1.00ct and costs noticeably less, because the price steps at the number, not at the millimetre. And do not dismiss faint fluorescence — it is discounted out of habit rather than out of any visible effect in most stones.

Every round here carries its original GIA or IGI report, and every one can be viewed in 360° before you commit.