Dispersion (fire) in diamonds and gemstones
Dispersion is the splitting of white light into spectral colours as it passes through a gem, because each colour bends by a slightly different amount. Fire is what you see as a result: flashes of coloured light from a cut stone. Diamond's dispersion is 0.044, enough to give a well-cut stone strong fire.
3D Jewelry Designer1 min read
How dispersion is measured
A gem bends violet light more than red. Gemmologists quote dispersion as the difference between its refractive index for the two, at the Fraunhofer G line (violet) and B line (red). For diamond it is 0.044.
Sapphire, ruby and emerald disperse light much less, and a strong body colour masks much of the fire they have.
What makes fire visible
Dispersion belongs to the material; how much fire you see depends on the cut and the light. Facet angles decide how far the colours fan out as light leaves the stone. Spotlights and direct sun bring fire out, while diffuse light, such as an overcast sky, mutes it.
Fire is judged alongside brilliance, the white light a stone returns, and scintillation, its sparkle as it moves.
Fire in a 3D render
A renderer shows true fire only if it bends each colour by its own amount.
The studio renders diamonds with real refraction, dispersion and fire, lit by an HDR environment you choose for the gems separately from the metals (background, lighting and ground). The free 3D jewellery renderer uses the same engine and materials on your own file, and jewellery rendering covers stills and video.
Questions
Does more fire mean a better diamond?
No, not on its own. A good cut balances fire with brilliance, and unusually colourful flashes can point to moissanite or cubic zirconia, which disperse light more than diamond.
Related
- Refractive index: how diamonds and gems bend light
Refractive index measures how strongly a gemstone bends light. What diamond's index of about 2.42 does for brilliance, and how a 3D render uses it.
- Diamond brilliance: what it is and how cut affects it
Diamond brilliance is the white light a polished stone returns to the eye. How cut creates it, how it differs from fire, and how a 3D render shows it.
- Jewelry rendering software that runs in your browser
Photoreal jewelry renders in your browser: diamond refraction and dispersion, auto-detected metals and stones, stills up to 4K and turntable video.