# Any jewelers out there ?



## TomVader (Nov 12, 2013)

I've been playing around with lost wax casting and would love to talk to a jeweler about some problems I've been having. Any response is appreciated.


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## Dan Dement (Nov 12, 2013)

Tom,

We specialize in casting Resins in Pd & Pt. Do it everyday for over 10 years. What's your problem?

Dan


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## TomVader (Nov 12, 2013)

I'm starting out simple and want to make a 14k wedding band. I made a silicone mold of my ring and cast a wax copy, sprued it up and invested. I burned it out and poured in the gold. The rings keep coming out with pits in the surface. Everything I read says that pits are either caused by imperfections in the wax model or improper casting temps. I've been very careful that my models are perfect (or nearly so) and that I'm following the instructions that came with the investment. When the first few came out with pits, I began adjusting the temps. First the mold temp. at casting, then the maximum burnout temp., and finally the temp. of the gold. I must be missing something, because I've run out of variables.
Here are the specifics:
Burnout temp. 1250 - 1350F
Flask temp. 1020 - 1230F
Gold temp. 1650 - 1830F
Any advice will be greatly appreciated, Thanks.


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## TomVader (Nov 12, 2013)

...I forgot to mention, I'm using a Kerr 900 kiln for burnout and a Hardin electric crucible furnace for melting metal.


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## Lou (Nov 12, 2013)

How long are you burning out for?

Also, metal might be gassy or your investment mix (which investment) not porous enough to allow all the gases out.


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## Palladium (Nov 12, 2013)

Just a thought but have you questioned the purity of the gold or alloy your using?


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## FrugalRefiner (Nov 12, 2013)

Is the gold you're using refined gold you are alloying yourself each time, or are you remelting 14 K gold? The pits could be porosity from oxidized base metals.

Dave


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## Palladium (Nov 12, 2013)

Silver has a known affinity for oxygen also. ?


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## TomVader (Nov 12, 2013)

Thank you all for your attention.
I'm roughly following guidelines for burnout. The kiln I have heats up very slowly, so 1hr on "low" gets me to about 350F, long enough for the wax to melt and run out onto a tray. Then I turn it up to "6", which over about three hours gets to about 1300F. I leave it there for an hour and then turn it down to "3", it then cools VERY slowly to casting temp.
I've been remelting 14k.
I've used two brands of investment; SRS Premium and Americast.
I'm degassing the investment with a vacuum table, and also pouring molten metal on my vacuum table. The vacuum table is one I've made myself, basically it's a steel plate on legs with a hole in the center. A copper tube is sealed to the underside of the table and ends in a valve. A PVC hose then runs to an air conditioning service pump. My vacuum chamber is a short length of plastic pipe 8in in diameter with a piece of heavy plexiglass covering one end, and a bead of silicone rubber around the opposite rim. It's quite airtight.
What gasses can be dissolved in molten gold?
Thank you all again.


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## TomVader (Nov 12, 2013)

Palladium,
I'm using scrap gold that I buy and sell, I test everything with a scratch stone and acid. That's as accurate a test as I'm capable of performing. If there's some impurity in the gold that's causing these pits, then I don't really have a way of knowing what it could be, short of refining it and examining the remains. Thanks.


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## Harold_V (Nov 13, 2013)

I refined for jewelers for years. For the record---precious few of them were willing to risk casting with used gold (for more than one reason), and very few melted their gold more than once, aside from re-using the sprue from a previous casting. A large portion of the gold I processed was exactly what you've been using, and almost always contains solder, which can contribute to poor results. 

As you continue to melt gold, the base metal (copper in yellow gold) oxidizes and can result in inclusions. They may manifest themselves as the pits you described, but tend to be more like "smudges" in the polished surface. If you've melted the same gold numerous times, that may, indeed, be your problem. 

You can minimize the rate of degradation of the gold you melt by keeping a reducing atmosphere with the flame of your torch. It won't be as hot, but it will protect the base metal(s) against degradation. 

If your gold is responsible for your problems, you won't be able to improve your results with the same gold unless it is refined, or enough clean gold alloy is added to the button to thin the bad gold adequately. I don't recommend that procedure, as it's akin to washing your car with muddy water.

Harold


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## TomVader (Nov 13, 2013)

Thank you Harold. I am melting in an electric furnace in a graphite crucible, but I know this doesn't keep out 100% of the oxygen. I will continue my efforts with a homemade alloy. I have two .9999 fine ingots that I can use. If that doesn't solve the problem I'll search for another variable. Thank you.


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