How do I fix weights where many bones overlap, such as the face, using Multi-Paint, and when does it refuse to work?

Problem. Where more than three bones influence a vertex (mouth, eye loops), painting one bone at a time breaks the balance. Conditions. Blender Weight Paint mode, Armature tab with at least two pose bones selected. Method. Enable Multi-Paint: the brush then edits the combined weight of the selected groups and keeps their ratio. Combine with locking: select a loop of bones with Multi-Paint to edit the falloff between the loop and its neighbours, and lock the neighbours with Lock Relative to edit falloff inside the loop (the manual calls this two independent one-dimensional gradients). With Auto Normalize on, the combined value is the sum of weights; otherwise the average. Failure modes. Multi-Paint cannot paint vertices that have no weight in the selected groups and will not reduce the combined weight to zero; X Mirror is symmetrical only if the weights already were. Workaround from the manual: with vertex selection, run Smooth Weight (Selected Pose Bones, low Factor) to copy a nonzero distribution from neighbours, then paint. Limitations. Documentation only; no quality numbers. Version/date. Blender manual main branch as fetched. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Documentation only; effectiveness on AI-generated faces (often with ambiguous topology) is not measured. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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  "citations": [
    {
      "url": "https://projects.blender.org/blender/blender-manual/raw/branch/main/manual/sculpt_paint/weight_paint/tool_settings/options.rst",
      "note": "Multi-Paint; Multi-Paint; Normalized Weight Workflow (tip); Multi-Paint (tip)"
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    {
      "url": "https://projects.blender.org/blender/blender-manual/raw/branch/main/manual/sculpt_paint/weight_paint/introduction.rst",
      "note": "Multi-Paint; Multi-Paint; Normalized Weight Workflow (tip); Multi-Paint (tip)"
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