The hollow face
It will not stay hollow
A hollow mask is a three-dimensional object. Look at the concave side and it typically flips back to looking like an ordinary, convex face.
Look at the hollow, negative version of a face mask and it immediately switches back into a positive, normal-looking face; you cannot hold the hollow view. Michael Bach: hollow face
Information about the three-dimensional world is lost when it is projected onto our two-dimensional retinas, and some retinal images can be interpreted in more than one way. Michael Bach: hollow face
If we cannot rely on shadows, there is nothing in the image that can tell us whether a face is really hollow or normal. Michael Bach: hollow face
Faces have a special relevance for us: throughout life we try to “read” faces, and when both a hollow and a normal reading are equally likely, the balance tips toward a normal face. Michael Bach: hollow face
A drawing is not a hollow mask
A flat drawing cannot do what a real hollow mask, or a carefully lit film of one, can do. The hollow-face claims on this site are about that three-dimensional case, as described by Michael Bach, not about the schematic section we drew to show the idea.
The schematic above is only a side view, to show the difference between a convex face and a hollow mask. It is not a substitute for a real mask or a film of one.