What is fire in a diamond?
By Jared James · Last updated 21 May 2026
Definition
Fire is the term for the flashes of spectral colour, reds, oranges, blues and greens, seen in a diamond or certain other gemstones as white light passes through the stone and is split into its component wavelengths by dispersion. It is one of the three optical properties used to assess a diamond's beauty alongside brilliance and scintillation. A well-cut diamond with good proportions produces plenty of fire, and you notice it most in low light when the rainbow flashes are vivid against the white sparkle.
Frequently asked questions
- What is the difference between fire and brilliance in a diamond?
- Brilliance is the white light reflected back from inside and the surface of the stone, while fire is the dispersion of that light into spectral colours. A bright diamond has both; very high fire with less brilliance can make a stone look colourful but less white and crisp.
- Do all gemstones show fire?
- No, it depends on the stone's dispersion value, which is a measure of how strongly it splits white light. Diamonds have good dispersion, but stones like sphene and demantoid garnet have even higher dispersion and can show extraordinary fire. Many common gems like sapphire and ruby show very little.
- Does cut affect fire in a diamond?
- Yes, significantly. A poorly cut diamond with wrong angles or proportions wastes light and produces less fire. An excellent or ideal cut optimises both brilliance and fire by directing light through the stone at the right angles.
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