I've experienced an oddity with my last two stone-in-place castings,
and none of my "casting buddies" seem to know why it's happening or
how to prevent it. The flasks, let me start by saying, were done at
two completely separate times, separate burnouts, etc. They were even
2 different batches of investment.
In both cases, a thin film of metal flowed over the surface of the
faceted stones. One set of stones were high-quality CZs. The other
were black diamonds. The size of the stones ranged from 1mm to 3mm
rounds. In each flask, the flow did NOT occur over all the stones -
roughly half were affected in each flask. None of the flow was over
the exposed pavilion of the stones - all were over the table and most
of the crown.
One theory was that the debubblizer liquid (I used very light sprays
on both flasks) created enough of a space over the stones to cause
the metal flow once the investment had set.
Another theory was that the stones expanded slightly during burnout,
then contracted, leaving just enough space for the metal to flow.
Both "sound" plausible, but I'd love to know:
1. Is this a common occurrence for stone-in-place casting? (I haven't
done all that much of it, yet.)
2. Is there a way to prevent it? Any idea why it's happening?
3. If it does happen, how would you repair it? (The thought of
grinding it off, given that it's on the entire exposed top surface
of the stones makes me fear damage to the stones using this