Dispersion
White light is every color moving together. Glass slows each one by a slightly different amount, so wherever its surface curves, they part ways. Move your pointer to pull at the glassTap anywhere to pull at the glass; scroll to change what it's made of.
Water
Refractive index 1.333, Abbe number 55.7
A rainbow is this effect at the scale of weather. Each raindrop sends red light back at about 42° and violet at about 40°, so the colors reach you from different rings of the sky.
Crown glass
Schott N-BK7. Refractive index 1.517, Abbe number 64.2
The everyday glass of lenses. A high Abbe number means low dispersion: colors stay close together, which is what a camera, a microscope or a pair of glasses needs.
Dense flint
Schott N-SF11. Refractive index 1.785, Abbe number 25.7
Heavy metal oxides make it bend light hard and spread it wide. On its own it smears color. Cemented to a crown lens, its error cancels the crown's, and the pair brings red and blue to nearly one focus. Telescopes have relied on that pairing since the 1750s.
Diamond
Refractive index 2.417, Abbe number about 55
Its dispersion is close to water's. The fire comes from the index and the cut: light meeting a facet more than 24.4° from straight on can't escape, so it bounces inside until it leaves through the top at a steep angle, where small differences in index become wide ones.
Rock crystal
Clear quartz. Refractive index 1.544, Abbe number 69.9
The original crystal. The Greeks called it krystallos, ice, believing it was water frozen too hard to ever thaw. Quartz barely spreads color on its own; the sparkle here comes from the cut. Dozens of small facets each catch the overhead lights and throw them back at their own angle, so every few degrees of turn sets a different group flashing.
It also splits light a second way. Quartz is birefringent: depending on its polarization, a ray meets an index of 1.544 or 1.553.
Make your own
Most clear materials fall between an index of 1.3 and 2.4, and an Abbe number of 20 to 90. The lower the Abbe number, the wider the colors spread.
- Light trapped beyond
- 38.1°
- Spread, nF − nC
- 0.0207
- Closest real material
- F2 flint
How this is drawn
There are no images or 3D models on this page. One fragment shader describes the glass as a distance field, follows each ray into it, bounces the ray off the inner faces when it can't escape, then refracts it out at seven wavelengths and blends them back into color. The shadow and its bright core are traced the same way. Dispersion is drawn three times stronger than life so it reads on a screen.
Measuring…