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Problems with pewter casting


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Hi, I know this forum is for blade smithing but I'm hoping you can help me with these problems I'm having casting pewter. 

I've been trying to make my own lead figurines. I've made a mold using Mold Max 60 and I've had moderate success, but now I'm running into some problems.

I'm melting all the material in a pot in my kitchen stove at home. In it there are some melted pewter figurines, some lead figurines, and an ingot of lead thrown into the mix.

The first few casts were pretty good, and they would be solid about 20 minutes after casting, but the latest ones are more fragile. Today a figurine broke in half while I was getting it out of the mold. It felt like dry mud almost. It had been cooling in the mold for approximately an hour, which a week ago was more than enough time for it to solidify.

Why are the latest casts so fragile, when the ones prior were stronger? Am I degrading the metal by melting it and remelting it over and over?

Also, I'm getting a ton of slag. It's all metallic, but it won't melt and I have to remove it from the pot. Can this be re-used? Is the stove too cool and that's why some of the mix doesn't melt?

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9 hours ago, Miguel said:

Hi, I know this forum is for blade smithing but I'm hoping you can help me with these problems I'm having casting pewter. 

I've been trying to make my own lead figurines. I've made a mold using Mold Max 60 and I've had moderate success, but now I'm running into some problems.

I'm melting all the material in a pot in my kitchen stove at home. In it there are some melted pewter figurines, some lead figurines, and an ingot of lead thrown into the mix.

The first few casts were pretty good, and they would be solid about 20 minutes after casting, but the latest ones are more fragile. Today a figurine broke in half while I was getting it out of the mold. It felt like dry mud almost. It had been cooling in the mold for approximately an hour, which a week ago was more than enough time for it to solidify.

Why are the latest casts so fragile, when the ones prior were stronger? Am I degrading the metal by melting it and remelting it over and over?

Also, I'm getting a ton of slag. It's all metallic, but it won't melt and I have to remove it from the pot. Can this be re-used? Is the stove too cool and that's why some of the mix doesn't melt?

The fact that you get a ton of slag probably indicates that you are getting it way too hot. You're burning up the metal, and what you call slag is probably oxides. This may also be much of what you are casting into the mould. The surface of the metal should look clean and shiny of the molten metal before you cast. I don't have much experience with pewter, mostly just pure tin, so I don't know all of the things that can happen in your case. However, f.e. zinc is also very brittle when cast. And also keep in mind that alloys in varying percentages can have a really big influence on castability and the material properties of the cast. So just mixing in various percentages can have all sorts of weird results. It's better to stick to an exact alloy that is suitable for the kind of casts that you want to make.

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Thank you for your reply, I hadn't considered that it might be too hot, I thought once I was pass the melting point everything was good. I'll get a laser thermometer and keep a closer eye on that.

As for the oxides, do you think they're reusable, or should I throw them away?

Would borax help with any of these problems I'm having?

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The oxides are a total loss, don't keep them.  Borax is for higher temperatures, use a tiny bit of beeswax as flux.  It will cover the surface of the melt and help prevent oxidation.  Right before you pour, take some stiff paper or a wooden stick and gently wipe the oxides off the surface of the molten pewter.  This will give you a clean pour.  If the surface of the molten pewter turns gold, purple, or white, you are too hot.  Add a drop of wax, then skim the surface.  

I melt pewter in an iron ladle.  I wax the hot iron, then add pewter.  As soon as it is fully liquid I skim it and pour.  I do this with pure tin, but it works well with lead-tin alloys as well.

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  • 3 weeks later...

I hadn't had a chance to try this out until yesterday. I got a laser thermometer and some beeswax and I can see clearly that indeed the melt was too hot, and the wax does a nice job clearing it up.

I'm still having a hard time getting the pewter to go into the fine details of the mold. I think I have to work on making better sprues in my molds.

Thank you both very much for your help!

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To get the fine detail fill out of your mold, you might try pre heating the mold.  I do a lot of cast bullet stuff mostly casting with wheel weights + 2% tin.  The extra tin helps the alloy to fill out and give nice crisp lines.  Also to get a good fill out of the base, be sure to keep a big hot puddle in the sprue.  When the alloy starts to cool, it will shrink some and if your sprue is liquid, it will pull from there to fill out the base.

Any pics of your molds and figurines?

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Thank you Glenn, I definitely think I need to work on making bigger sprues for my molds. The few molds I've made so far are very compact and didn't leave much room for that unfortunately. Also the intake hole in the mold is quite tiny, I'm sure that doesn't help.

I will try to make some appendages to these molds with a big sprue, I'd hate to throw them out, but the molds I make in the future will definitely have room for a nice big sprue.

My camera is on the fritz, I can't send pics sorry!

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Big sprue with tiny intake hole to the mold always equals bad casting.  That makes a spray effect inthe mold with tiny droplets that freeze before the mold can fill completely.  The gate (intake) should be nearly as large as the thickness to which it is attached.

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