Pewter Problem

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Pewter Problem

Post  Stu on Wed Dec 14, 2011 11:31 am

I've been casting pewter onto my pipes for about 5 years now and never had a problem till the other day. Normally it turns off nice and easy in short curls, this time fine powder sprayed everywhere!

Stubborn as I am, I did not just quit and perhaps figure out the issue first. I just kept at it; then the chanter snapped! I turned the air blue for a while, put my tools away and came in from the shop.

The metal acted as if it was crystallized. I use Britannia metal, tin/bismuth/antimony. Only thing I can think is I recover the machined off pewter and remelt it. Perhaps this is the issue? This particular batch has gone through about 5 times now; but with the now highish price of pewter, I hate to use it once and chuck, or give to a friend to make cheap jewellery as this batch is going.

Any thoughts folks?

Stu
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Re: Pewter Problem

Post  Yuri on Sat Dec 17, 2011 2:37 pm

All I can think of is that each time you melt the amalgam (cos that's what it is), there is some oxidisation. Visible as the "scum" floating to the top. Well, possibly the tin does oxidise at a different rate, so the proportions of the metals keep chnaging with each melt, and in the end you end up with something quite different from what you started with.
I only did this inlay a very few times, and none of them on bagpipes. I used ordinary solder, which round here is 50-50 tin/led. Works really well.
Touching on this whole thing, I even thought of trying silver, yes silver, of the tooth amalgam fame. I know a cabinetmaker has done inlays in amalgam in some headboards, so it is possible. Wonder if anyone did it in instruments? (amalgam doesn't even need melting, as anyone having spent some time in a dentist's chair will know.It's mostly silver/mercury, with these days minute additions on the lines of antimony, platimun, I don't know what, but these are really minute.)
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Re: Pewter Problem

Post  Stu on Sat Dec 17, 2011 7:18 pm

Yuri wrote:All I can think of is that each time you melt the amalgam (cos that's what it is), there is some oxidization. Visible as the "scum" floating to the top. Well, possibly the tin does oxidizes at a different rate, so the proportions of the metals keep changing with each melt, and in the end you end up with something quite different from what you started with.
That is kind of along the lines I was thinking. I've made quite a number of instruments with pewter and this has worked out quite well, till now.
Yuri wrote:
Touching on this whole thing, I even thought of trying silver, yes silver, of the tooth amalgam fame. I know a cabinetmaker has done inlays in amalgam in some headboards, so it is possible. Wonder if anyone did it in instruments? (amalgam doesn't even need melting, as anyone having spent some time in a dentist's chair will know.It's mostly silver/mercury, with these days minute additions on the lines of antimony, platinum, I don't know what, but these are really minute.)
Sounds like an interesting thing to try sometime. I'll have a look at what that costs.

Thanks

Stu
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Re: Pewter Problem

Post  marcblur on Wed Dec 21, 2011 8:09 am

When salvaging almost any metal for recasting, it's a good idea to use at least 50% fresh metal with it. Five melts is definitely going to leave you with a more crystalline, brittle structure. Are you using a flux when you do your melt? Even lard can work on pewter. Also, don't let the dross(scum) go into your casting. Dross is made of the oxides that make metal crunchy.

By the way, I wouldn't go near mercury amalgam silver. I've heard too many stories of people getting an amalgam piece they didn't know about, trying to recycle it and getting poisoning from the fumes. Nasty stuff if treated improperly.

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