Matched pairs: what a 2% tolerance actually means.

A pair of studs is the most unforgiving piece in the case. The two stones sit a face apart, in the same light, and a client who has never heard the word "table" will notice in a second if one looks bigger, flatter or warmer than the other. So when we say a pair is matched, this is what we mean.

Measurements first

Diameter decides whether the two stones look the same size. For rounds we aim for the two diameters to sit within a tenth of a millimetre of each other, both ways. For ovals and cushions, length and width both matter, and so does the ratio, because a slightly fatter oval next to a slightly longer one reads as two different shapes.

Table and depth within 2%

Table percentage and depth percentage describe the proportions of the cut. Two stones with the same diameter but a 55% and a 61% table return light differently: one has a tighter, brighter pattern of flashes, the other a broader, more open look. Within two percentage points of each other, the eye reads them as siblings. Beyond that, one will tend to look livelier than the other every time the client turns her head. Depth works the same way, and also governs how a stone faces up for its weight, so a 2% window keeps both the look and the apparent size together.

Colour, side by side

Two F stones can be a warm F and a cool F. Reports do not record that. We lay the stones table-down on a white folded card and compare them against each other, not against the master set, because the client will only ever see them against each other.

Fluorescence, the same

None next to none, or faint next to faint. A medium-blue stone paired with an inert one can look fine in the shop and mismatched at a window on a bright day. We will not send that pair, even if the reports read the same.

Report grades, close

We will pair an F with a G, or a VS1 with a VS2, when the stones look alike and it saves your client money. We will not pair stones from different laboratories in the same piece, because the invoice should read cleanly.

Weight, last

Clients ask for "a pair of half-carats". What they mean is two stones that look the same. We treat total weight as the last consideration, not the first, and we tell you if the better-matched pair is 0.96 ct total rather than 1.00.

How we show you a pair

One video, both stones together on the same tray under the same light, table up and then on their sides. Both reports, both measurements laid out next to each other, and the differences highlighted. If we had to choose between two candidate pairs, we tell you why we chose the one we are sending.

For studs, three-stone rings and side stones, brief the pair. Tell us the setting and the metal, and leave the matching to us.