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:
-
Is this a common occurrence for stone-in-place casting? (I haven’t
done all that much of it, yet.)
-
Is there a way to prevent it? Any idea why it’s happening?
-
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
approach.)
Many thanks!
Karen Goeller
@Karen_Goeller
www.nolimitations.com
Karen:
I’ve had it happen occasionally, so it’s not unique to you, although
usually mine were very thin flashes over parts of the CZ’s, rather
than the whole upper surface of the stone.
I don’t use debubblizer, so that’s not the culprit. My thought has
been that the stone shifted very slightly in the investment, due
either to a rough bounce when loading the casting machine, or thermal
expansion, or the simple malice of Murphy.
Cleaning them off wasn’t enough trouble for me to worry about it
overmuch. I used an engraving tool to peel up an edge of the
flashing, and then use the wedge-shaped front end of a flat graver to
peel it back far enough to cut off with another engraving tool. If
you’re totally covered, carefully engrave down towards the table of
the stone until you can start peeling it off.
If you get “the one true answer” about why this happens, let me
know. Meanwhile, this should help you clean them up a little more
easily.
Regards,
Brian Meek.
Another possibility is that if the waxes were cleaned with a solvent
(wax-kleen, naphtha, or other commonly used hydrocarbon or citrus
based product) after the stones were set in the wax, a thin film of
wax/solvent could be left on the surface of the stones, creating
enough of a space to allow metal to flow in the resulting void. If
this is the case, make sure all excess is wiped dry (a Q-tip is good
for this) before investing. Also, for this same reason, I wouldn’t
recommend using debubblizer for stone-in-place flasks.
Frank Reisser
Modelbuilders
Karen - i was wondering if you steam dewax your flask before burn
out - goo