How to buy gemstones and diamonds wholesale

Name the mineral and the variety, then say whether the stone is natural, laboratory-grown (synthetic) or an imitation. Laboratory-grown stones have the same chemistry as natural ones, so the difference cannot be judged by eye. Then ask which treatments the stone has had, such as heating, filling or irradiation. A treatment is not a fault, but it changes the value and must be disclosed.

Weight is given in carats, with dimensions in millimetres. Cut stones are described by colour, clarity and cut; for diamonds these join carat weight as the four Cs. Say how many stones there are and whether they are a single stone, a matched set or a mixed lot.

• Rough: bought on weight, shape, colour and the inclusions a cutter must plan around.
• Cut and polished: faceted stones and cabochons, sold by the carat, the piece or the matched lot.
• Mineral specimens and decorative stones: valued for species, locality, size, condition and look rather than carats.

An independent gemmological laboratory can identify the material, separate natural from laboratory-grown or imitation, measure weight and dimensions, describe colour and clarity, and detect treatments. Some reports also give an origin opinion. Read the scope of every report, check that the report number matches the stone, and confirm it with the laboratory that issued it. A report is evidence, not a guarantee of price.

Ask where the stone came from and how it changed hands. Expect supplier identity checks, sanctions and restricted-party screening, export and import permits, and customs classification. Rough diamonds are covered by the Kimberley Process Certification Scheme, and other categories can carry their own rules. Requirements differ by country and by stone, so take advice for high-value lots.

• The price basis: per carat, per piece, per kilogram or per lot, and the currency.
• Payment terms and when title passes.
• An inspection or return window, and who pays if a stone is not as described.
• Insured courier or hand-carried delivery, and who pays duties and import taxes at destination.

• A price far below the market for the description.
• No documents, or documents that cannot be confirmed with the issuer.
• Pressure to pay quickly or to skip testing.
• A refusal to let an independent laboratory examine the stone.

Ragtrail connects businesses. It does not hold gemstone inventory of its own and does not issue certificates. Material offered through Ragtrail is sourced in the first instance from Verdaan Gems & Stones and described lot by lot with the documents that exist. See Diamonds, gems and precious stones trade, follow the journey of a gemstone in 3D, or browse the Gems & Stones department.