I have been centrifugal casting with a silver /copper mix
(50/50). The castings come out rough/ pebbly.
The investment is the standard Kerr material, formulated pretty
much to the instruction sheet. The burn out is much longer as I
have been burning out twigs and little plastic pieces. Had a lot
of bad castings when only burning out for eight hours as I still
had sections of wood in the casting (lost a bunch of three ounce
I cannot tell if the problem is overheating of the alloy or
residuals of plastics/organics in the flask. The extended
burnout is the same for plastics/organics for sterling silver
castings without getting the rough surface. The pieces polish up
well enough. Seeing this problem in writing makes me think that
the burnout cycle is still too short or not at high temperature
soak long enough.
Type of plastic or organic material is anything that has a shape
I guess a wax could be made of the plastic pieces and the problem
would go away except that is an unwanted interim step.