Greetings,
Is there a formula to calculate how much metal (22-karat gold) is needed to fill the hollow space in a Delft clay casting impression?
The only way that I know how to do this is the displacement method.
Fill up a graduated cylinder (or some kind of container) to a specific water level (say 200 ML). Attach your model to a thin wire by wrapping a small part of it. Submerge your model into the graduated cylinder and water. Make a mark to where the water level rises to. Remove your model and add metal until it gets to second water level.
This method is fairly accurate, but if your model isn’t waterproof this won’t work. It also seems to work better with a narrow container, which is why I like graduated cylinders.
Because you’re casting 22 kt, the cost implications of a mistake are fairly high. Have you been practicing casting sterling silver? I’d definitely recommend getting the process down, but I’m sure you’re on top of that.
Let’s see if anyone has other ideas.
Best of luck!!
Jeff
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Remember that you need a lot more metal that that which will fill the hollow space. You need enough to fill the sprue neck and hole. Delft clay is fun, but because of the texture that it leaves, you do have to remove a lot of metal to finish the piece. Working with 22K, this will be an expensive process. Take Jeff’s suggestion and get the steps down in sterling first…Rob
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I do a small amount of Delft Casting too. And only in sterling. If I am carving wax or creating my originals in some other material the displacement method works very well for me. I use a beaker from a cooking supply as my measuring device. They generally will have demarcation lines in ounces or some other option. This method of measurement works fine for rings, earrings, components on pendants and bracelets. I haven’t tried a belt buckle yet.
Consistency in how you create your casting is critical with your sprue allowances. If you always allow the same amount of space in the mold for a sprue your allowable metal will generally be the proportionate to your casting. Remember to allow additional metal to travel up the vents a well as the sprue.
Experiment a bit in sterling first.
Don
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After thinking more about your question, I should have said that it depends on what your model is made of. If your model is made of jeweler’s wax for lost wax casting (like carving wax) the traditional formula is to weigh your wax and multiply that weight times the specific gravity of the metal that you’re using.
Jeweler’s wax has a specific gravity of 1. 22 kt gold has a specific gravity of 17.5. So if your wax model weighs 1.5 grams, then you’d multiply that times 17.5.
1.5 x 17.5 = 26.25 grams of 22 kt.
Like Rob mentioned you still need to add metal for the sprue and button.
If your model is something other than jeweler’s wax then I think you’ll probably want to do the displacement method.
To be clear you can also use the displacement method on carving wax etc, but you asked for a formula and that’s the formula that is used in lost wax casting.
Like everyone in this thread is saying casting 22 kt is going to be very expensive and any errors will be costly. The specific gravity of sterling silver is 10.4. If you’re going to practice casting silver.
If you’re looking for a good reference book on many jewelry casting processes including sand casting, Tim McCreight’s Practical Casting is a good one.
Hope all that helps!! Let us know how it works out!!
Jeff
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Excellent. Thank you for the information.
I appreciate the help.
Kind regards,
Lois
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