Hello friends!
I’ve been casting silver at a hobby scale for some years now. But I’ve got an opportunity coming up to help a couple make wedding rings, and they want to cast in gold. I worked with gold once, almost 20 years ago, and it was a fabrication class not a casting class.
I did some browsing in the archives, but I’d love your suggestions too: what will be different about casting gold vs silver? (I’m anticipating 18k yellow but I haven’t confirmed yet.) What are the beginner’s mistakes I can avoid?
We’ve got a fresh crucible, a programmable burn out kiln, and a choice between centrifugal and vacuum casting. They will probably work on waxes first, weigh them and purchase casting grain from Rio, and then we will cast and finish together.
Again, I’ve done plenty of silver casting and I’m confident in that arena, but I don’t know what I don’t know about gold.
Thanks!
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My first suggestion would be to buy your gold from somewhere else. Rio is pretty expensive and I have been unimpressed with the performance of their alloys. Stuller or United PMR would be a better source. They cost less and have more choices in color and alloy characteristics. UPMR’s tech support will also help you and offer advice if you have any trouble.
That said 18k yellow isn’t particularly difficult to cast, but temperatures should be accurate. For that reason I recommend melting it in an electric furnace and using a vacuum machine.
Common pitfalls I can think of off the top of my head:
Getting your casting temperatures wrong, either resulting in shrinkage porosity or incomplete fill.
Flask temperature too low or high, creating the same effect as above. Verify with a test before you go for a full pour. UPMR has data sheets for each alloy that you can use as reference.
Improper spruing which creates turbulence or non-progressive filling of the mold. Results in porosity, tears and cold shuts. All connections should have a fillet. No right angles.
Improper burnout in the early stages - you don’t want anything to boil whether it be wax or water in the investment. This creates poor surface quality. I bench cure for 3 hours and the drying phase in the oven is 3 hours.
Not having enough metal for the button and sprue. I find that when casting just one or two rings, I often need more grain than I thought to keep the metal flowing well.
A less common but still possible mistake is using a flask that is too small. The models should have at least 1/4” clearance from the wall.
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