shape
Carat is the weight unit for diamonds. 1.00 carat equals 0.20 grams
Clarity
Measures the presence of internal inclusions or surface blemishes. The purer the diamond, the more light passes through it and the higher its value.
Overtone
Coloured diamonds often show shades of a secondary colour, called an overtone. A diamond with an overtone is generally less valuable than a pure-colour stone — but not always: a yellow with a pink overtone can cost more than the same diamond without it.
Yellow without overtone
Yellow with orangy overtone
Intensity
Hue, saturation and colour uniformity are the key factors in fancy diamonds, far more important than carat or clarity. The more intense and vivid the colour, the more precious and rare the stone.
IGI, GIA and HRD are the most reliable certificates.
Polish
Describes the quality of finish on the outer surface of the diamond. A high grade maximises light reflection and brilliance.
Symmetry
Evaluates how precisely the facets align and intersect. Minor asymmetries can affect light travel and brilliance. Excellent and Very Good are recommended.
Fluorescence
About one third of natural diamonds emit a completely harmless bluish glow under UV light. Fluorescence rarely affects appearance; in very rare cases it may cause a slight milky effect.