Pouring an Ingot

Russ Jones

“Obscure information central here, how may we be of service?”  

“Yes, if I pour an ingot of metal, how much would it weigh?”

“Not enough information, please restate the question.”

“Uh, yeah.  If I pour an ingot of my metal, how much would I have?”

“What size is your ingot and what metal are you pouring?”  

“Uh, I’m using the small round one and I think I’ve got some silver, but there might be some nickel in there too.”

Ok, so the conversation sounds outlandish, but I’ve actually been asked this in a similar conversation more than a few times.  There are a lot of variables to this question so I thought I’d address it as well as I can, giving the math behind the answer and some of the methods I’ve used to solve it.  That way, you can use the information I’m presenting you to give you a starting point for figuring it out for your situation.

The first thought, besides just pouring metal and weighing it, was to pour wax into the molds I use and weigh them, then convert the wax mass into metal mass. (Yes, I know my terminology is a little less than precise...I’m not a physicist.)  But after doing that, I found that the accepted specific gravity of wax is an estimate and that I wasn’t accounting for shrinkage. So I went to a more accurate estimate.

Durston combination ingot mold

The first step was to take the ingot mold I use and mathematically determine the nominal volume of each ingot.  I say nominal because the given measurements in the sales literature are very close to reality, but not quite there.  In the end, this method will give you an appropriate starting place for pouring an ingot. Also, unless you’re well practiced, you’re going to spill a little anyway, so round up.  For all volumes, I used centimeters as my unit of measure to make my end math easy. I recommend the same. If you’re using Durston’s ingot molds, they’re made using metric measures anyway.  For the round wire molds, volume is 𝜋r2h; for rectangular, volume is lwh.  I added a small amount to account for spillage, a small button, and shrinkage.

Durston combination ingot mold

The next step is to simply multiply the volume of each ingot mold by the specific gravity of the metal you’ll be pouring.  Ok, that’s not exactly an accurate statement, but it works. The reality is that you need to convert specific gravity into density, but because we’re using cubic centimeters in our volume measurements, we only have to multiply the specific gravity by 1 gram per cubic centimeter in order to give us our units of measure.  

So to recap, find the volume of your ingot, then multiply by the specific gravity of your metal.

V=𝜋r2h  or V=lwh (in cm)

m=Vp (mass=volume x density)

Check out the chart for the results on the Durston Ingot Mold I use.  

What do you think, Francis?  

I know, math hurts, but it was the easiest way to explain this.  And I couldn’t come up with any obscure music references to reference for this.  Let’s go pour some heavy metal, Francis. You know, it’s your one way ticket to midnight.  Fifty thousand watts of power…

P.S. The chart is available as a pdf.  Just email us.

an 79mm x 10mm round ingot of sterling silver

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