IOR (index of refraction)
Index of refraction, a number describing how much a material slows and bends light as it passes through.
Typical values
| Material | Approximate IOR |
|---|---|
| Glass | 1.50 to 1.52 |
| Quartz, amethyst, citrine | 1.54 to 1.55 |
| Emerald | 1.57 to 1.58 |
| Topaz | 1.61 to 1.63 |
| Spinel | 1.71 to 1.72 |
| Sapphire and ruby | 1.76 to 1.77 |
| Cubic zirconia | 2.15 to 2.18 |
| Diamond | 2.42 |
| Moissanite | 2.65 to 2.69 |
Why IOR matters for jewelry
A high IOR gives a small critical angle, so light inside the stone reflects off the pavilion facets instead of escaping. That is the basis of brilliance. Diamond's IOR of 2.42 is why a well cut diamond looks so much brighter than glass cut to the same shape.
IOR in renders
In a renderer, IOR controls how rays bend when they enter and leave a gem, and how strongly the surface reflects at glancing angles. Using a glass IOR for a diamond produces a dull, see-through stone, while using a diamond IOR for a sapphire overstates its brightness.
The gem presets in the RenderMyJewels studio set refraction and dispersion together for each stone type, so choosing a ruby preset gives ruby-like optics as well as ruby colour. Some gems, such as sapphire and moissanite, are doubly refractive and have two values. Renderers usually use one average value, which works well for product images.