You've got your sunken & your high/low relief —
let's say you carve
a monster of gold-veined jade
using each technique.
The finished pieces,
one statuary, one mask,
replicate each other in both figure & presence,
but do not reflect at all.
The statue is caught in a flash of presence;
its stone soul makes it a simple object
Utterly and completely unreal.
The mask instead forces its observer to become
that same stone figure, utterly without identity,
in that initial unscripted first glance through the emptiness of
suchlike a shell as we all inhabit.