ZBrush Tip: Mask By Cavity — Precise Crevice Masking for Paint & Polish

Mask By Cavity quickly isolates crevices so you can target detail, paint, and polish with precision.

• Where to find it: Tool > Masking > Mask By Cavity. One click generates a mask based on recessed areas (valleys/crevices).
• Core idea: Use the automatically generated cavity mask to protect or affect micro valleys without touching surrounding planes.

Quick workflow

• Prepare: Work at a subdivision level where your cavities are actually present. On very low-res meshes, consider subdividing or using Sculptris Pro to add local tessellation before masking.
• Generate: Tool > Masking > Mask By Cavity. If the effect feels subtle, repeat once or twice to strengthen the selection.
• Refine: Use BlurMask for softer falloff, SharpenMask for crisp isolation, and Grow/Shrink to adjust coverage depth along the crevices.
• Target either side:
  • Keep as-is to protect cavities while you polish, flatten, or paint raised surfaces.
  • Invert the mask to affect only the crevices (ideal for grime, AO tints, oil, and shadow tucks).

Practical use cases

• Edge wear pass: Mask By Cavity, keep the mask as-is to protect recesses, then lightly HPolish or TrimDynamic to break up broad planes and emphasize highlights on peaks.
• Grime and dirt: Mask By Cavity, Invert, switch to Polypaint, lower RGB intensity, and glaze darker tones into crevices. Finish with BlurMask and a soft brush for natural diffusion.
• Controlled noise: Invert a cavity mask, apply Surface Noise or a tiling alpha at low intensity to add micro buildup only in recesses.
• Safe retouch: Keep cavities masked while using Move or Inflate for form tweaks so you don’t collapse panel lines or pores.

Enhancements and combinations

• Peaks instead of valleys: Try Tool > Masking > Mask PeaksAndValleys if you need raised edges more than deep creases.
• Group it: After generating a cavity mask, use Group Masked/Group Unmasked to create fast polygroups for iterative selection and UV seam planning.
• Non-destructive: Apply paint or material changes on Layers so you can dial back cavity effects or toggle them during review.
• Render support: Pair your sculpt with BPR AO and Cavity passes for comp; they reinforce the same visual logic you established with masking.

Troubleshooting

• Mask too weak/strong: Repeat Mask By Cavity or follow with SharpenMask/BlurMask. Use Grow/Shrink to fine-tune how deep the mask reaches into folds.
• Geometry too simple: Add subdivisions or leverage Sculptris Pro to ensure there’s enough curvature detail for the detector to latch onto.
• Performance: Hide unneeded SubTools and work on visible portions to keep masking responsive on heavy scenes.

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