Catmull-Clark: From Pixar Faces to Jewelry CAD

In 1978, Edwin Catmull and Jim Clark published a way to turn a rough mesh into a smooth surface: Catmull-Clark subdivision. You start with few faces. The algorithm refines them. Edges soften. The shape stays editable from the coarse cage.

Decades later, that idea powered digital characters. Soft cheeks, eyelids, cloth folds: the same math that made Pixar faces look alive also became a standard for organic modeling in CAD and animation tools.

What the math actually does

A Catmull-Clark step splits faces, averages points, and pulls the mesh toward a limit surface that is smooth almost everywhere. Designers do not think in the formulas. They think in a control cage: push a vertex, the smooth surface follows. Keep the cage light and the form stays editable. That is why subdivision became the language of organic CGI.

NURBS still rule precise jewelry construction: shanks with exact finger size, bezels with known wall thickness, stones with carat tables. Subdivision does not replace that. It fills the gap NURBS hate: flowing volumes, soft blends, and character that feels sculpted rather than patched.

Why jewelry CAD cares

A lion head on a signet, a softened cathedral shoulder, a carved leaf on a pendant: hard NURBS patches fight you. You either accept a stiff look or export to a sculpting program and fight the round trip back into a manufacturable file.

Subdivision lets you think in volumes and then refine, closer to how wax behaves on the bench. The cage stays simple. The surface gets the smoothness the eye wants. Production still needs thickness, clean topology and a path to mesh or NURBS for casting. The win is doing the organic work on the same piece, not in a second world that forgets jewelry rules.

Rhino SubD, then RhinoArtisan

In Rhino, that world is SubD. You model with a controllable cage, then smooth toward a surface you can keep working.

In RhinoArtisan 7, SubD sits inside the jewelry workflow, not beside it. Sculpt turns solids, surfaces, SubD or meshes into digital clay, with live minimum thickness so organic work stays castable. Relief carves printable depth from images. Text to 3D turns a description into a mesh you bring in and refine with Sculpt, next to settings, shanks and manufacturing tools.

Catmull-Clark began as a paper about smooth surfaces. In the workshop it becomes a practical answer: organic form without leaving the piece, and without redrawing it for production.

Full picture of organic tools in 7.0: What’s New in RhinoArtisan 7.0.