Two-Part Mold (pt 1) and a New Favorite

While I'm happy with my new one-sided mold technique, I've been eager to try to cast in lead.  The disadvantages (expense of metal, expense of extra silicone, exposure to molten metal, ease of use of water-putty) far outweigh the advantages (durability, painting) but I'd still like to try lead casting just to see if I can do it.  I sculpted a new spaceship that I'm so enamored with, I figured I'd go ahead and sacrifice some extra silicone to make a two-part mold.

I like this sculpt; hopefully I can reproduce it in metal

The ship is already buried under curing silicone, so tonight I sculpted a similar design to illustrate the process.  I start with a press mold in Sculpy as before, but this time I encase the polymer clay in a LEGO box. 

Not my favorite design..

I pour water-putty into the box and let it set for 100 minutes or so.  I carefully remove the LEGO box and I'm left with the top hull of a spaceship with attached channel for hot lead (far right) and keys to line up the two silicone mold halves.  I put the LEGO box back together around this cast and get ready to pour the first half of the rubber mold.  And I'm off to mix silicone.