How to render diamonds realistically

What makes a diamond look real?

• Brilliance: white light returned through the top. Diamond's high refractive index makes light inside the stone reflect off the lower facets instead of escaping; glass of the same shape leaks far more.
• Fire: flashes of colour. Diamond bends each colour of light by a slightly different amount, which is dispersion.
• Scintillation: the pattern of bright and dark flashes as the stone moves, which needs dark areas in the lighting.

How do you set up the diamond material?

1. Set the index of refraction (IOR) to about 2.42, with no tint or roughness for a colourless stone.
2. Allow enough internal bounces. Light reflects several times inside a diamond, and too low a bounce limit (often called ray depth) leaves the facets dark or black.
3. Turn on dispersion. Without it the stone sparkles white but shows no fire.

What lighting does a diamond need?

Contrast. Use an HDR environment with bright, defined sources, such as softboxes or strip lights, against darker space; even lighting leaves the stone flat. Small, bright sources bring out fire. Rotate the environment until the top of the stone catches a highlight, and keep exposure low enough that highlights do not clip to white. A little bloom reads as sparkle; too much blurs the facets.

Does the 3D model matter?

Yes. Facets must be flat with crisp edges; if an export smooths the shading across them, the stone looks moulded, not cut. The stone must be a closed solid, so the renderer knows where light enters and leaves. And a pavilion cut too shallow or too deep leaks light in a render, just as a real stone does.

How does the studio render diamonds?

In the studio, an uploaded file gets materials and lighting by default: stones are detected from the file, gems get real refraction, and diamonds get dispersion and fire. Coloured stones keep their saturation instead of turning grey or black. Gems, metals and two-tone finishes covers changing a stone.

Light comes from a fixed studio rig plus swappable HDR environments, with separate choices for gems and metals. You can rotate the environment in the studio; embeds and share links keep it unrotated. The Advanced panel holds exposure, tone mapping and, from the Starter plan, bloom (background, lighting and ground).

For a final still, a beauty render combines many slightly offset frames into one image, sharper than the live view on facets and metal edges, at up to 4K. It is on the Growth plan and above and uses 4 credits (camera and capture). The free 3D jewellery renderer runs the same engine on your own file with no account; more in jewellery rendering in the browser.