[yarcob]

> Why would you not just print a negative directly - as indeed she later does? Is it because she considers the concave surface difficult to sand smooth?

I think the problem with sanding a mold is that it would be very hard to sand both halves equally, so you'd end up with a step where the two halves meet.

Using the wax to smooth the mold when the two halves are already stuck together is quite ingenious, as the wax will also smooth the part where the halves meet.