Normals (3D)
Vectors that describe which direction a surface faces, used by renderers to calculate shading and reflections.
Face and vertex normals
Each polygon has a face normal. Vertices can also carry normals, which are blended across faces so that low polygon surfaces look smooth. This smoothing is what lets a round shank look round without millions of triangles.
Common problems
- Flipped normals. A surface pointing inwards can render black or invisible, depending on the renderer.
- Over-smoothed edges. Smoothing across a sharp edge, such as the corner of a bezel or the facets of a stone, makes it look soft and melted.
- Faceting on curves. Too little smoothing on a curved surface shows flat bands.
Normals on stones and metal
Gem facets must stay flat, with hard edges between facets, so each facet reflects light as a crisp plane. Metal curves need smooth normals across the surface but hard edges wherever the design has a crisp corner. Most export dialogs and 3D tools let you set a smoothing angle that keeps edges above that angle sharp and smooths the rest.
Fixing them
In Rhino, consistent surface directions before meshing avoid most problems. In tools such as Blender you can recalculate normals so they face outwards and mark sharp edges. If a part renders black in the studio, check its normals first, then check for a duplicate surface sitting in the same place.