Gem materials
GemGpu's stones are ray-traced through real faceted geometry — dispersion, internal bounces, body color, and fire behave like the physics, not like a shiny approximation. This chapter is the Material tab with a gem part selected (or the gem family active with nothing selected).
Presets first
The fastest route is the library: Gems ▸ pick a family (Diamond, Corundum, Beryl, Quartz, and more) ▸ click a tile. Diamond alone ships the D-to-Z color journey (D Colorless through Light Yellow), the fancy colors (Yellow, Blue, Pink, Green, Brown, Black), and no-fire variants; colored stones cover Ruby, Sapphire, Emerald, Aquamarine, Morganite, Amethyst, Citrine, Garnet, Alexandrite, Peridot, Tanzanite, Topaz, Tourmaline, Zircon — plus Birthstones by month and Cabochon cuts.
With a gem selected, the preset applies to that stone alone. With nothing selected, it becomes the look for all gems and the template new gems arrive with.
Applying a preset never wipes your per-stone geometry corrections (Cut cleanup below) — looks and fit are kept separate on purpose.
Optics
The heart of the stone:
| Control | What it does |
|---|---|
| IOR (1.2–3) | Refractive index — how strongly light bends. Diamond is 2.417; moissanite higher; glass lower. |
| Dispersion (0–0.2) | The rainbow fire. Diamond's physical value is subtle (0.01-ish); push it for drama. |
| Ray bounces (0–10) | Internal reflections traced per ray. More bounces, deeper sparkle, slightly heavier rendering. |
| Reflectivity | Surface reflection strength at the facets. |
| Transmission | How much light passes through versus reflects. |
| Gem reflections | The stone's own exposure to its environment — brighten the world inside the gem. |
Body color
- Color grade — the D-to-Z diamond scale as one slider; it drives body color and density together, calibrated per grade.
- Body color — direct color for fancy or colored stones.
- Density — how strongly the body color saturates with depth. Deep stones drink more color.
Light return
Fine control over what comes back out: Tint color (cast on returned light), Fire color (tints the dispersion flashes), Gamma (contrast inside the stone).
Inclusions
Real stones aren't perfect, and a hint of interior life reads as authenticity — especially for emeralds, rubies, and natural-look diamonds:
Surface roughness, Veil strength / coverage / roughness, Feature scale, Fracture relief — together they build interior veils and features from subtle silk to a dramatic included look.
Cut cleanup
Per-stone geometry corrections for imperfect meshes: Squash (fixes slightly stretched cuts) and Geometry blend (how faithfully to follow the raw mesh versus the idealized trace). These stay put when you change looks — they belong to this stone's mesh, not the material.
Custom materials
Dialed something worth keeping?
- Save current as custom (in the panel) keeps it in your quick list.
- Save new gem to Drive stores it as a named document in your Drive — with a live thumbnail captured from your viewport — available on every machine.
- Export / Import JSON moves a material as a file for sharing outside your account.
- Star any library tile to keep it in Favorites.
Copy & paste between stones
Right-click a stone → Copy material, then right-click another → Paste material. Pasting onto a part of a different kind converts it first, so the result is always what you expect.