Gemstone sourcing for jewellery designers and brands

A dealer can only find what is described. A useful brief separates what is fixed from what can move, so that a stone a shade lighter or a fraction of a millimetre smaller is offered rather than missed.

• Species, and the variety where it matters.
• Colour, ideally against a reference: a photograph, a stone you already have, or a paint-up.
• Cut and shape, with the dimensions in millimetres the setting needs, not only a carat weight.
• Quantity: one stone, a pair, a suite or a parcel for a production run.
• The treatments you will and will not accept, and whether a laboratory report is required.
• What the stone is for: a one-off centre stone, a collection, or a run that has to be repeatable.

Collections need stones that agree with each other. A matched pair for earrings has to match in colour, size, cut and the way light comes back from it; a suite for a necklace has to graduate evenly; a parcel for a production run has to stay consistent across the run and be available again for the reorder. These are harder to find than a single fine stone, and a parcel is often gathered from more than one dealer, or cut to match.

Matching is judged with the stones side by side, in the same light. Photographs taken separately, under different lights, hide differences a customer will see across a counter.

Some designs need a stone cut to a drawing rather than chosen from a tray. Fantasy cuts, carvings and flush inlays are commissioned from the cutters who do that work and nothing else. The rough is read before anyone commits to it, because the drawing and the crystal have to agree about where the colour sits.

A custom cut is specified like a component: outline and dimensions, the depth the setting allows, the facet style or the carving, and the tolerance on each. An inlay adds the metal’s side of the drawing, because a stone set flush into a ring’s face and the recess it sits in are made to fit each other.

Ethical sourcing begins with knowing what a stone is and what has happened to it. Many coloured gemstones on the market have been treated, by heating, oil or resin filling, diffusion or irradiation, and some treatments change a stone’s value and its care far more than others. UK consumer law treats leaving out information a buyer needs as misleading, and the trade’s own standards require treatments to be disclosed.

Diamonds move under the Kimberley Process and the trade’s System of Warranties, which address conflict diamonds. Coloured stones have no single equivalent, so their provenance rests on the documents and the dealers behind each stone. Gemlea’s brief records what may have been done to a stone, and stones are offered with what is known about them.

A laboratory report identifies the stone, says whether it is natural or synthetic, and names any treatment the laboratory detected. An origin report goes further, but it does not say where a stone came from. It says which origins the evidence is consistent with, and how confident the laboratory is: two quite different claims. Read a report for the identification, the treatment line and the exact wording of the origin opinion, and check that the stone in hand matches the weight and measurements printed on it.

Gemlea Source also searches the auctions against your brief, whether for gems or vintage and estate pieces. Each catalogue is read with a gemmologist’s eye: what a lot actually is, what the description does not say, and what it is worth bidding to.

For a designer, an estate piece can be a finished jewel for a collection, or a source of old-cut stones with a character modern cutting does not give. The hammer price is not the whole cost: the buyer’s premium, and VAT where it applies, are added, and both belong in the bidding limit.