Ray tracing
A rendering technique that traces the paths of light rays through a scene to calculate reflections, refraction and shadows.
The basic idea
For each pixel, the renderer sends a ray from the camera into the scene. When the ray hits a surface, it spawns new rays for reflection, refraction or shadow checks, and the light they bring back decides the colour of the pixel.
Why jewelry needs it
Jewelry is a showcase for exactly what ray tracing does well. Polished metal is a near perfect mirror, so reflections must be traced. Gems bend light on the way in, reflect it many times inside and bend it again on the way out. Without traced refraction and internal reflection, diamonds look like grey glass.
Ray tracing, path tracing and real time
Path tracing is a form of ray tracing that samples many random light paths per pixel and averages them, which handles soft light and indirect bounces well but takes time. Real-time renderers, including browser-based studios, usually combine fast rasterisation with traced effects where they matter most, such as gem refraction, so results appear in seconds instead of minutes.
What to look for
Good results show crisp, accurate reflections on metal, bright and dark facets in stones and clean shadows where the piece meets a surface. If stones look flat, check the gem material and its IOR before blaming the renderer.