I have a ring that people order from me quite a bit and it is a
constant source of frustration.
The ring is a heavy men’s ring. It is a signet ring with a skull on
a raised round face with a thin raised border around it. I also add
black enamel around the skull (inside the raised border)
Every single time I cast this ring, I wind up with some sort of
porosity behind the skull (inside the shank, directly behind the
front, or occasionally off to the sides at the heaviest part of the
I am vacuum casting, and using have used an atmospheric air/acet.
torch (prestolite) as well as my electric smelter.
Here is the trouble shooting I’ve done…
Ranged my flask casting temps from 900 up to 1200
Ranged my silver casting temps from 1790 to 1820
Tried a variety of different sprue methods ranging from the
"accepted standard" to several much less conventional methods. (i can
give more info here, but this could get a bit long)
Every single time, I wind up with pinhole(s) in the surface that
when ground and probed deeper prove to be massive hollow caverns
under the metal. It doesn’t appear to be gas porosity, as the holes
don’t appear so much as bubbles as jagged craters. It also doesn’t
appear to be shrinkage porosity as I supply a mass of metal to the
parts in question via sprues or the rest of the bulk parts of the
Often, I could get some solder into these spots except that after
the cast, I have to fire these pieces near 1500F to fire my enamel,
and this, of course, degrades any but the hardest IT solders.
I use Kerr Satincast 20 and follow their investment mixing schedule.
I have used everything from 50/50 old/virgin silver up to 100%
Here is my CURRENT burnout sequence. As stated earlier, I have tried
a variety of different temps for both the silver and the flask.
2 hour - ramp/hold at 300F
2 hour - ramp/hold at 700F
4 hour - ramp/hold at 1350F
1 hour - ramp hold at 1200F
I spoke with a gentleman at Rio Grande and he said to try all of the
things I’ve listed here that I had already tried.
This is one of my best selling rings, and I would hate to drop it’s
production. I have been casting for about 2 years and while I have
run into some issues at times, nothing this bad.
Any advice or info you folks could give would be a huge help.