I do a lot of these, very successfully. Put a piece of stiff wire in
the mould, use piano wire or titanium, I use 1.6mm mostly, it needs
to be highly polished and make sure that the section where the bead
goes is straight. The far end away from where you inject is bent
around in a ‘u’ shape and when you cut open the mould you stop
cutting before you get to the ‘u’. The mould therefore stays in one
piece, with keys cut only at the front and the wire poking out from
the uncut part.
When you extract the wax twist it slightly to ease it off. A little
mould release wiped on the metal rod occasionally will help.
For small beads, 4mm, run the sprue down to one side of the wire
core, for 8mm you would probably be better doing two sprues, one down
either side. The principle is that you flow the molten metal along
the length of the plaster core rather than at right angles to it, so
as to put less stress on it.
I have enjoyed learning about this, I now do long thin beads, large
hollow beads cast in one piece, and curved holes through. I would
recommend a stereo microscope for the finest detail.
I have though about writing up my methods, everyone else seems to be
writing books! I just thought it was a bit of a niche in a niche,so
only a very small audience, you really also need to do your own
mouldmaking, wax injecting and casting.
kind regards Tim Blades.