> Thought I speculated that there would have to be two masters.
> Also moulds do not have to be containment. Clay could have
> been flattened down onto one mould [...] Excess clay would
> not have to be trimmed off as the clay would not necessarily
> have to fill the moulds to their edges. [...]
In this case, the resulting disk should have a convenient white margin,
because clay is not transparent, so there is no way of putting the second
mould exactly in the correct position.
On the contrary, in both faces, the signs of the outer circles are very
close to the edge. The disk is not perfectly circular, still the signs seem
to "follow" the edge, on *both* faces.