Did you try my recommendations? They come right out of Stuller’s
book… They state, the larger the ring, the higher the temp. Try
calling Stuller and ask them for help with their product.
This is pretty obvious, so forgive me if this sounds too
simplistic. Are your crucible and stirring rod clean? Is the
metal cleaned of all foreign matter? I steel brush all buttons,
and grind when necessary. Old silicon creates problems.
The acetylene concerns me, I cast with oxy-hydrogen when torch
melting, and get consistently better results.
I had the same problem and it vanished when I raised flask and
metal temps… I also switched to vacuum casting all large
castings, there is much less turbulence which helps on large
Have you ever tried waxing a ball next to (but not touching) the
ring ? it helps with shrinkage problems. One more thing, the
sprue can be too heavy… it should be about the same thickness
as the ring, just ever so slightly larger. Otherwise, it creates
a hot spot at the juncture that creates shrinkage porosity.
Aurthur Avalon (King Aurthurs Court Casters) use to use
rectangular sprues back in the 70s, they really work great, you
might try getting away from the round sprues.
The bad spots in the carving wax patterns are a mystery to me.
Maybe you could hold the flask at about 400 until the carving wax
is evacuated, and be sure not to put it in the oven before it has
had a chance to fully harden (at least one hour). You could be
experiencing steam erosion problems with the investment. If you
are building up the carving wax with a hot pen, you could be
putting air bubbles under the surface that suck investment, and
you might not see them because they don’t break the surface,
gotta be careful with those. You might try NOT vacuuming (the
second vacuum step) one flask that doesn’t require it (vibrate
it) and see if the problem persists, you could narrow it down
this way. One more thing, if you oven has lost its calibration,
you could be overheating the investment at the highest
temperature, you might try restricting the upper temperature to
1200 one time and see if that helps.
I get great castings using Stuller’s gold, even castings
weighing up to an ounce. My tree castings are usually porosity
free too (referring to gent’s rings).
One important tip, DO NOT MIX ALLOYS! (sorry about the yelling)
I have experienced many problems resulting from mixing alloys
from different manufacturers.
One side note, I usually don’t use Stuller’s alloys, I use the
mix from AAA Precious Metals (Portland OR). I think it’s the best
in the business, and their 18k yellow and super white alloys are
the best as well. (my personal opinion)
Jeffrey Everett, jewelry craftsman
Handmade 18K, 22K, and platinum gemstone jewelry.
Diamond setting, rubber/metal molds, casting, lapidary
Die and mold engraving, plastic patterns for casting.
Jewelry design, cad/cam, milling, scroll, filigree, & more.
P O Box 2057 Fairfield IA 52556 515-469-6250