I am joining this discussion a little late.
I usually burnout 2.5 inch flasks containing injection wax and
Ferris blue carving wax. I usually pour up to 150 ounces of sterling
silver per casting cycle.
I turn large pieces of pottery in Blue carving wax which are around
3.5 inches in diameter and up to 3 inches high. Some times I will
have one to three 4 inch flasks filled with turned bowl of Blue
Ferris carving wax in the oven. Each flask might contain up to around
50 grams of wax. I once cast a flask containing 65 grams of wax.
Carving wax melts out of the flask at a higher temperature than does
My over is 12X12X10. I do not cast until I have enough flasks to
completely fill the oven. The 2.5 inch flasks are usually stacked
I have a programmer to control the temperature. I vacuum cast.
I put the flasks into a ambient oven and heat it up to 250 degrees
and hold that temperature for 2 hours. I then increase the
temperature around 150 degrees per hour. My oven has a difficult time
heating up any faster. I will force it to increase up to 300 degrees
per hour when I can.
I start the BO cycle around 3:00 pm. The oven usually reached 1300
degrees around midnight.
I always maintain the flasks at 1300 degrees for at least 8 hours.
The flasks always come out bone white. If I have a large amount of
carving wax in the flasks I will burn out longer period of time.
I usually start the cool down to 860 degrees around 8:00 to 9:00 the
Black smudge on the investment of the flasks is usually a sign of
I vacuum cast sterling silver an melt the metal in a handy melt
All sterling silver castings will develop fire scale because of the
temperature the metal experiences during the metal cool down cycle.
I have gotten around the problem of getting fire scale on my
castings by following the anti fire scale procedure I developed by
accident several years ago.
The process is simple. I generate a reducing atmosphere around the
cooling flask after it is removed from the vacuum table.
The process, which is describe in the following two Orchid papers,
is very simple. The process works so well I do not find it necessary
to spend the extra amount for anti oxidization silver.
I no longer pickle the castings and have had some castings come out
so clean I was able to go directly to polishing with Jewelers Rouge
once the sprues were removed
I now cast sculpture in sterling silver without the fear of getting
fire scale on my projects.
If you vacuum cast sterling silver you might want to look up the two
My guess is that the process would work for casting any copper base