anyway, if anybody knows why my investment and castings are so
yellow, please give me a clue.
Overheating would be tending to break down the investment, which
you'd see most prominantly as a rougher surface, not necessarily a
yellowish color. Silver can easily be quite black when first removed
from the investment, so that doesn't by itself, suggest anything.
You say the investment looks yellow before casting? That suggests
incomplete burnout. What sort of wax are you using? Some plastics,
though usually not standard casting waxes, might do that. And if the
kiln doesn't have sufficient air flow through it, you might be
getting incomplete oxidation of burn out products, leaving surface
discoloration. That would certainly affect the surface of the
You might still be overheating. It's possible for controllers to be
miscalibrated. An easy check would be to set the max temperature a
bit lower. There's not a tremendous difference in burnout ability
between 1300 and 1350, so if your system is accurate, at 1300 you'd
likely get as good a burnout, but if your system isn't calibrated
right, it might be getting hotter than 1350, which might cause
problems. I'd try reducing the max temp by fifty degrees to 1300, as
well as extending the time spent at the max temp. Be sure also that
the kiln you're using was intended for casting burnout. Some kilns
sold for enamelling, or for PMC, are not well enough ventillated to
give a proper burnout. Some of them might require something like
additional holes drilled, perhaps in the top of the kiln into the
heating chamber (be sure to avoid heating elements!), to give better
exhaust of burnout products. A check for this would be to try a test
burnout with the door of the kiln not completely closed. Leave it
just cracked slightly open, just a couple millimeters, enough so a
very little bit more air gets around the door seal, rather than
actually swung open, since then it would never heat up all the way.
But very slightly ajar, maybe just with the latch not quite closed,
should let a little more air circulation happen without preventing
proper heat up. See if that makes a difference.