Free tools for labeling jewelry 3D models include Blender (for visible on-model text) and MeshLab (for hidden metadata like SKU or material).
Blender lets you create and position text directly on models (e.g., brand names or size markings). MeshLab adds searchable metadata to organize models.
For beginners, use Blender’s "Add > Text" for visible labels or MeshLab’s "Filter > Quality Measures and Compute > Edit Metadata" for hidden tags—both work with common formats like OBJ or STL.