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Sterling ingot bubbles

After working with Argentium for a long time I wanted to melt sterling into ingots. However after trying many things and retrying with fresh sterling nothing works.

How I do it:

  • reversible Durston mould
  • oxy propane
  • oil the mould and heat it up until it smokes
  • preheat the crucible
  • heat up the sterling silver and use the borax cone to flux it (I used borax salt as well in other tries)
  • when it is molten and water like I pour it through flame
  • separate the mould faces (it smokes) and I quench the ingot

The result…as in the attached picture (in other tries smaller and multiple bubbles present)

What am I doing wrong and what to change in this process?

Casting sterling silver ingots can be an exercise in frustration. After a lot of trial and error, I have developed a process that works for me. If you look at the Links page of my website (www.robmeixner.com), you will see two PDFs that describe how I cast sterling silver in both a two piee metal ingot mold and Petrobond Sand…Rob

That’s two “piece” not two “piee” ingot mold. When you discover a bubble or blister or split along the edge or even in the middle of an ingot as you roll it, you can work around it, depending on what you plan on using the ingot for. Being able to recycle your scrap is great, but it is very labor intensive and may not always be the most efficient way to go. Goog luck…Rob

Rob: Nice tutorial! I had a problem with my ingots splitting/cracking, and I didn’t forge them as they were so small I didn’t think I’d need to. I will next time! Oddly enough, the fine silver ones didn’t need the forging (didn’t crack).

Thank you for your answer. I went through the pdf and it’s good advice.

I have a question about forging though: if the silver ingot has pits and bubbles inside, will forging fix that? I mean, those little spaces will still be there (compacted after forging though) and will be eventually exposed when rolled. Am I right?

With argentium silver I never had such an issue. I could melt it, pour it, roll it, no problem whatsoever. However, I have about 30 oz of sterling lying around. I thought I could put that to good use (if not for actual pieces, at least I learn how to melt sterling haha)

I am not a metalurgist so I can answer your question. I have also never worked with argentium. Once in a while I will get what I call blisters when the ingot is rolled to 20 gauge or thinner. They appear after an annealing operation. They can be rolled down, but when I start to sand or grind they reappear as a very shallow pit, but can be quickly removed and polished over. My guess is that they are bubbles of some sort. I don’t know why they appear. This is one reason why I polish an ingot once I am done rolling it. This also makes later polishing operations easier with less chance of distorting the shape while polishing after the ingot is cut, sawed or punched into smaller shapes. You do have to do what you can to prevent fire scale if you are doing any soldering. I have been making some pieces of totally rivetted jewelry lately and this prepolish works very well for that. I would like to try some argentium some time. Thanks…Rob

After many days of frustration and no ingot without inclusions and as any inclusions inside will eventually cause cracks I gave me one task only, to find a way to pour usable ingots.

After tens of pours and lots of reading on the subject I finally succeeded to pour inclusion free ingots consistently. I will not point the whole process out, instead I will point out what I changed and I believe fixed the problem.

  • heat the mould even more
  • tip the mould more, like to make the molten metal roll down along the wall of the mould and not “fall” to the bottom
  • pour slower, don’t rush it
  • the flame…this I think is an important part. As the flame acts like a wind, the way I held it before (oriented towards the base) was forcefully pushing the molten metal into the mould, creating turbulences. I now hold it to cover the molten metal as I pour and orient it towards the crucible (I found that this will also stop borax from getting into the mould)
  • after it is poured I keep the flame on the opening of the mould for two three seconds more, while also increasing the fuel

As you can see there is no easy answer, all the conditions have to be perfect in order to get that perfect ingot. But if I were to choose one, perhaps pouring slower and have it rolling down the wall would be the most important part.

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Here is an ingot that is perfect and with no cracks while rolling it. It also had no visible inclusions on the inside under 10x magnification.

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Nice ingot/bar.
I’m happy you found a way :slight_smile:

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Finding what works for you is half the battle. Looks like a nice ingot…Rob

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