The first physical step is typically the creation of a skull model — a precise physical reproduction of the skull, usually in resin, based on a high-resolution CT scan.

This model becomes the foundation on which the face is built.

Building the musculature comes next.

Clay or similar material is used to represent the major muscle masses of the face — the masseter, the temporalis, the zygomaticus, the orbicularis oculi, and dozens of others.

The sizes and positions of these muscles are inferred from the attachment points visible on the skull, from the general proportions of the skull (which correlate with muscle size in predictable ways), and from anatomical reference.

The muscles define the underlying shape of the face.