Facet doubling is the double image of facet edges seen through a strongly doubly refractive stone. It shows clearly in moissanite under a 10× loupe.
In more detail
Look through a crown facet at an angle, not straight down through the table. Along the optic axis, nothing doubles. Doubling proves that a stone is not diamond. It does not prove moissanite, because other doubly refractive stones double too.
How we measure it
The 3D Gemstone Simulator traces both rays, so moissanite's edges double in its render at an angle.
Related terms
- Doubly refractive: A doubly refractive stone splits light into two rays that vibrate at right angles and travel at different speeds. Each ray has its own refractive index.
- Birefringence: Birefringence is the difference between the two refractive indices of a doubly refractive stone. It shows how strongly the stone splits light into two rays.
- Optic axis: An optic axis is a direction in a doubly refractive crystal along which light does not split into two rays. Seen along it, the stone behaves as if it were singly refractive.
- 3D Gemstone Simulator: The 3D Gemstone Simulator is a free Digital Gemology tool that renders a cut stone as a camera sees it. You choose the cut, gemstone, carat weight, color, clarity, cut grade and lighting.