- Colour
- The dominant driver of value, by far. Gemmologists read it as three things at once: hue (ideally a pure green, or green with the faintest hint of blue), tone (neither so light it looks washed out nor so dark it goes lifeless) and saturation (the vividness of the green, which matters most of all). A rich, evenly distributed, vivid green is what commands the premium.
- Clarity
- Almost every natural emerald contains inclusions, the French trade calls the effect jardin, a “garden” of fissures and crystals grown into the stone. In emerald these are expected and accepted; the benchmark is “eye-clean,” meaning nothing distracting is visible to the naked eye. A large emerald with no inclusions at all is cause for suspicion, not celebration, usually a sign of a synthetic or a substitute.
- Cut
- Because the rough is brittle and often fractured, cutting emerald is a craft of protection as much as brilliance. The step-cornered emerald cut was devised precisely for this stone: its broad, calm facets reduce stress on the crystal and open a clean window onto the colour. A good cut balances weight retention against the even return of light.
- Carat
- Fine emerald is rare in larger sizes, so price per carat can climb steeply as weight rises, a five-carat stone of top colour is worth far more than five one-carat stones of the same grade. Size is never read in isolation from the other three.
