Corn starch works fine as a mold release. The only drawback I
suppose, is that it might have a tendency to dry out your clay if
you’re not done working with it right after the molding is done.
The thing with sterling is that when embedded in metal clay the
sterling becomes brittle and breaks off – this is especially
noticeable when the wire extends beyond the clay.
Apparently the problem is the 75/1000 parts of non-silver stuff in
the sterling, that causes the problem. If you want to use sterling,
you have to solder it on after the clay is fired.
Chicago area, Illinois, USA
Metalsmith, Certified PMC Instructor
Studio 925; established 1992