V-Ray Tip: VRayOverrideMtl Clay Pass for Accurate Lighting Evaluation

Need to evaluate your lighting without the noise of textures and complex shaders? VRayOverrideMtl gives you a clean, reversible “clay” view while preserving critical ray interactions.

Practical setup (fast and safe):

• Create a neutral “middle gray” VRayMtl:
  • Diffuse color: linear 0.18 (roughly sRGB 0.5 / 128,128,128)
  • Reflection: 0 (off) to avoid specular bias
  • Refraction: 0 (off)
• Add a VRayOverrideMtl and wire it as follows:
  • Base material: your neutral gray (for a true clay pass)
  • GI material: same neutral gray (ensures indirect illumination is unbiased)
  • Reflection material (optional): original material, so reflected objects still look “real” while staying clay-lit
  • Refraction material (optional): original material, to keep believable transmission through glass
  • Shadow material: neutral gray (consistent shadowing)
• Assign the VRayOverrideMtl to the test objects or a duplicate of the scene for non-destructive comparison.

Why VRayOverrideMtl over a global material override:

• Granularity: Override GI, reflections, refractions, and shadowing independently.
• Context retention: Keep mirrors and glass showing the original materials while the lit surfaces remain clay. This reveals light directionality and intensity without texture distraction.
• Selective exclusion: Leave emissive, glass, or hero assets untouched while “claying” the rest.

Best practices for robust lighting tests:

• Use mid-gray 0.18 to judge exposure objectively and avoid chasing highlights caused by bright albedos.
• Exclude critical materials:
  • Glass/Portals: maintain accurate light transport; exclude from overrides where necessary.
  • Emitters/VRayLightMtl: don’t override, or you’ll misread brightness balance.
  • SSS and volumes: either exclude or test separately; clay overrides remove their energy absorption and can skew GI.
• Turn off denoising for evaluations; denoisers can hide problem areas you need to fix with lighting.
• Use Render Elements (Lighting, GI, TotalLight, SampleRate) to pinpoint hotspots, leaks, or underlit areas.
• Compare with VFB History: store A/B snapshots of clay vs full materials to confirm improvements.

Reading the results:

• Check for smooth gradients on walls and ceilings; banding or patchy areas suggest insufficient bounce or poor light placement.
• Evaluate shadow density and direction; adjust light size and distance to soften or sharpen as needed.
• Validate exposure using a physical camera and real-world EVs; the clay pass should look balanced at your intended output.

Common pitfalls:

• Forgetting to restore materials—use scene states, material overrides lists, or a temporary scene copy.
• Clamping during tests can mask fireflies; avoid until final.
• Texture-driven light (projected gobos, emissive decals) won’t show if you override them—exclude intentionally when needed.

Ready to integrate this into your workflow or need licensing advice? Consult the experts at NOVEDGE for V-Ray solutions, upgrades, and pro tips. For streamlined purchasing and support, visit NOVEDGE.