Guide
Diamonds & Gemstones — Valuation Guide & What We Accept
The four Cs, coloured stones, and what really drives the price — a plain-language guide to diamond and gemstone valuation.
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Sell diamonds & gemstones →Diamond grading
Understanding the four Cs
The GIA's four-C grading system — carat, colour, clarity and cut — is the universal language of diamond valuation. Each C affects price independently, but the combination of all four determines a stone's true market value.
One carat equals 0.2 grams. Price per carat rises steeply at certain thresholds — a 1.00ct diamond commands a significant premium over a 0.95ct of identical quality.
D–F is colourless and most valuable. G–J is near-colourless and represents the sweet spot for value. K–Z shows increasing tint. Fancy coloured diamonds (vivid yellow, pink, blue) follow a separate pricing scale entirely.
Flawless (FL) and Internally Flawless (IF) are exceptionally rare. VS1–VS2 (very slightly included) is the most popular tier for fine jewellery. Inclusions visible to the naked eye (I1–I3) reduce value significantly.
Cut quality affects how brilliantly a diamond reflects light. An Excellent or Ideal cut can dramatically increase a stone's visual appeal — and its price. Poor cuts waste carat weight on depth that doesn't produce brilliance.
Coloured stones
Precious coloured gemstones
Sapphires, rubies and emeralds are graded on different criteria from diamonds — colour saturation, origin and treatment history all carry significant weight. A Burmese unheated ruby of fine colour can be worth more per carat than a comparable diamond.
Sapphire
Colour and Kashmir/Ceylon origin are primary value drivers
Ruby
Burmese origin and 'pigeon's blood' red colour command top prices
Emerald
Colombian origin and vivid saturation are key; inclusions (jardin) are accepted
Alexandrite
Dramatic colour change makes fine specimens exceptionally rare and valuable
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