QuestionI am just beginning jewelry making and lapidary class at our local park. Is there a formula for knowing the correct amount of silver to melt for a cast or mold. I am currently working on a couple of wax ring molds, and do not want to buy too much silver, but don't know how much would be enough.
AnswerChris, thanks for this question and best wishes in jewelry work. It is really neat to get the first few finished pieces done and be proud of the work.
Are you familiar with specific gravity? This is a comparison of how much mass something has compared to an equal volume of water. We do it easier and use the word "weight" instead of mass.
Casting wax is considered to be very close to a specific gravity of 1. All you need to do is multiply the weight of the wax by the specific gravity of the metal to be cast and you will get the weight of metal needed to fill up that space from the wax.
I will give an example below but first, here are your numbers:
Sterling Silver 10.36, just use 11
14k Gold use 13
Example: the wax weighs 0.75 grams. To cast in sterling is 0.75 x 11, which is 8.25 grams. You can use either grams or pennyweight, just use the same scale for the wax and the metal conversion.
So, to cast the wax you need 8.25 grams of sterling. Ahh..remember, this is just exactly enough to fill the void left in the plaster when the wax is gone, filling the volume of that space.
You need to weigh the sprue wax, too. And, you need enough metal to form a button of metal on the flask when cast. The button helps push the metal in and provides metal for the other metal to feed from as it freezes just when cast. Add from 1/3 to 1/2 more metal to the weight of the model and the sprue and you should be fine, a casting with a full mold, a nice sprue and a button you can cast again when mixed with fresh metal.
If this is confusing, let me know. You can use the follow-up to get back to me. Keep in mind, you can always add more metal and that is why I simply round off the specific gravity numbers to the next higher number. If you have too little metal, the mold is not fed enough metal and a poor casting is the result.
God Bless and Peace. Thomas. March 6, 2008 7:57pm
