So I have been playing around with mask → extract shell to create printable negative moulds. However it tends to cut back into itself ruining the surface of the mould. I have tried to then use a copy of the original piece as a hollow and then voxel merge it with the shell, but that kind of messes up the surface as well, for some reason. Any tips to work around this?
Why are you trying to make a shell?
Why not make a cube around the sculpt, then subtract the sculpt out of the cube? Then you have your negative.
I have done this as well but a shell would really allow me to do larger more cost (and time) effective prints