Interesting what a little zinc can do

[RogerDat]

I had some pewter that was contaminated by zinc handle on an item. I was chopping the stuff up with a torch and by the time I realized that one item was melting "weird" it was already in the melt.

So I had them tested to get the percentage of tin and zinc. And it was 9% on the zinc end. Well I got to thinking and decided I would see what percentage of zinc I would end up with if I made a normal pot of WW's with 3% Sn with 3% Sb.

To get that 94/3/3 was going to take:
1# mono/foundry type
1# contaminated pewter 89/7/4 misc. Sb & Cu
30# COWW lead

Zinc percentage was 0.29 and yes even that small amount made a difference.
What I got was a constant sludge on top, no point in scrapping it off as more would form so I just pushed aside and ladled from the cleared spot.

The ingots from this seemed to pour ok if a little bit odd flowing. The pot was constantly covered with a frothy sludge. Heat source was a propane turkey fryer and cast iron dutch oven. I was running pretty hot but did notice hotter seemed better. Neglected to measure temperature.

I ended up leaving a few pounds of slush and such in the pot to cool. So even if I gain something from the use of the contaminated alloy I will probably lose some weight in the process. Unless I find a temperature that reduces the froth back into the melt.

I have heard of people working with lead having up to almost 4% zinc contamination, would love to hear what they use for temperatures if known. I'm thinking even my 0.29% might yield a harder alloy which could prove interesting. If I can make it work. Right now I'm not sure but it seems like the loses outweigh the gains but we shall see.

I'm going to try the resulting alloy in a .310 RB mold and see what it looks like. Heat will be hot plate for the mold and Lee 20# melter and ladle casting. Will have a thermometer to record the melt temp. Will report back here with further results.

[Hickory]

That's bad.
You might end up losing a lot of tin getting out the zinc.

[lightman]

I would keep diluting it down until it cast ok.

[Time Killer]

Flux the contaminated zinc with sulfur it will help to draw most of it out. Its gonna stink so be prepared for that.

[kevin c]

Duly noted.

I have put a couple years and a fair amount of cash into building a store of pewter that I want to melt into user sized ingots. I would hate to contaminate a lot of it (I have enough that I am contemplating batches of fifty pounds or more). I will paraphrase the advice I got here from a couple long time pewter "repurposers": melt the flat touch marked stuff first (unlikely to have a hard zinc part), scrupulously maintain the pot temp well below zinc's solidus, ruthlessly cull anything that doesn't melt promptly on being added to the melt.

Rogerdat, if I may ask, just what was that zinc handle attached to, and was it marked as being pewter?

[JonB_in_Glencoe]

This thread has some good info in it.

I list some temperatures in post #6 when casting with the alloy containing 1% Zinc.

https://www.artfulbullet.com/index.p...let-alloy.589/

[popper]

Zn is good stuff. Did some tests with Zn 1%, Cu 0.5%, pure for 40sw (180gr Lee - 4.5 hp38) & 30/30 (185GC 16gr 2400). IIRC temp was 730-740F. 40 sized small so I got some side ways on target & leading (BLL coated). They expanded very well, some leading. Shot a pig carcass with the 30/30, 30 cal in, 40-45 out (gut shot) but the shoulder shot broke stuff and didn't make exit hole. Accuracy for both was actually pretty good. Hit running pig (hiney shot) with the 185GC in BO pistol, same alloy, got blood on the johnson grass but never found the pig. Zn allows hgher pressure without brittleness and they cast fine.

[RogerDat]

The item was marked pewter, it was a tray. The handle bases appeared soldered on. But the block that was the base for the handle and the handle were the problem from what I could tell. Tray wouldn't fit in my smaller pewter pot so I laid tray across and cut into slices. Handle slice was in the pot and under the tray getting hit by torch as I cut the next couple of slices off the tray. The handle melted when was hit by torch but remainder was not melting after tray did. I wasn't thinking at first so I hit it with a torch until I saw it wasn't flowing the way tin does, light bulb went off and I fished the remains of both handles out. I also normally melt pewter on a hot plate but these were all large bulky items so I put the pot up on my propane fryer.

Smallish batch of pewter, maybe 5# so I might try some garden Sulphur (outside!!!) to see how much zinc gets removed. Since the metal is essentially tin and zinc any loss of tin that goes with the zinc will still mean tin percentage goes higher, even if weight goes down.

I figure I can probably cast with the ingots I made, the Glenn B temperature info should prove useful for that. Might do some 30-30 that gets PC'd which should help with smaller diameter if that is an issue. Or .31 round ball for use as buckshot where size reduction won't be a problem.

Won't go out of my way to use this pewter as is, will try to use my 30# test batch of 94/3/3 just to see what it does. I have been lucky for the most part. Have done a fair amount of pewter over the years, probably close to 50# a year and this was the first ***** batch. It is one good reason to work in smaller batches.

Most of the pewter I do is hallmarked or at least stamped pewter/zinn. From time to time I will get something not marked or not readably marked and either melt on it's own where I can observe if it flows like tin when it melts so it gets thrown in with solder scraps or melt by dipping in pot of melted wire solder or small ends of bar solder where pewter should melt if just dipped in. I'm going to have the solder batch tested so will typically boost that tin percentage. Picture frames used to be an item I would find that was a pewter alloy but not always stamped, now they are all hard junk metal.

Using the contaminated tin I lost 2.5# as slush and gained 3% (or some percentage anyway) of tin in the remaining 27.5 lbs. or WW's out of 30 lbs. I started with. If Sulphur doesn't work to clean out the zinc from the tine then fine, I'll make tin/zinc round balls for slingshot ammo. No lead so safe to handle.

[kevin c]

Thank you for the description!