Hi, I'm new here and found this site via google. I am wondering if there is anyone out there who has successfully removed zinc from their lead? I have done a lot of fluxing but not sure if I have done enough, I also have a yellow colored oxide showing up that I have not seen before. Any input is welcome. The link I found to this site was from 2009. I'm hoping someone from that conversation can help me out. Thanks!
contaminated ingots HELP!
- Thread starter smoke17
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Bmac1949
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try castboolits.com. The guys on that forum can probably help.
mmorris
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beat me to it.
evan price
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The yellow/golden/straw colored oxide is NOT zinc. It is tin oxides. You are running your pot temperature too high when smelting your lead and it is rapidly oxidizing the tin out of the alloy. If you have been skimming it off, remelt it in your lead at a temp under 700 degrees and flux it aggressively with a good hydrocarbon flux- the tin is the expensive portion of the alloy and it's a waste to skim it off.
Straw/golden colored oxides form when the pot/lead temperature is high enough to cause surface oxidation of the top of the melt. Hotter temps cause faster oxidation. Rainbow/blue/purple/yellow colors are lead oxides, at too high of temperature. If you have alloyed metal that just needs ingotized there is no reason to run your pot hotter than 700 degrees especially if there is a possibility of zinc getting into the mixture.
One way to test for zinc is to take a sample of your suspect metal and let it cool. Then drip some acid on it. Many toilet cleaners are acids...I use The Works toilet bowl cleaner in the white angled spout-bottle, blue top. IIRC it is 20% hydrochloric acid. Drip it on zinc and you get a fizzy reaction like water and pop rocks candy. Less zinc, less fizz. Even mostly clean lead alloys will fizz a tiny bit I find if you let the acid sit on it a while- But zinc makes it foam quick.
If you did really have zinc- If it wasn't thoroughly overheated- you can remelt your ingots slowly, keep the temp under 700 degrees. Once you get to 700 and everything is liquified, let the pot start to cool down. The lead will stay liquid, the zinc will try to solidify into a chunky oatmeal-like dross that will keep floating up to the top. It will look like partially solidified foamy grey stuff. You can skim it off the top of the pot. Hold your pot temp at this temperature (between 650-700) and stir and flux with a good hydrocarbon flux- parrafin wax (candles, crayons, etc), used motor oil, etc. and stir the alloy well making sure to scrape the sides and bottom of the pot to bring all the zinc to the surface. Then just skim it out until you have mirror-bright liquid lead in the pot, and recast your ingots.
A little zinc (1% or less well-alloyed) won't hurt your bullet casting alloy except to make it seem tin-starved and not want to fill out the mold. It also hardens the lead up a bit. More than that and you get a mess.
Straw/golden colored oxides form when the pot/lead temperature is high enough to cause surface oxidation of the top of the melt. Hotter temps cause faster oxidation. Rainbow/blue/purple/yellow colors are lead oxides, at too high of temperature. If you have alloyed metal that just needs ingotized there is no reason to run your pot hotter than 700 degrees especially if there is a possibility of zinc getting into the mixture.
One way to test for zinc is to take a sample of your suspect metal and let it cool. Then drip some acid on it. Many toilet cleaners are acids...I use The Works toilet bowl cleaner in the white angled spout-bottle, blue top. IIRC it is 20% hydrochloric acid. Drip it on zinc and you get a fizzy reaction like water and pop rocks candy. Less zinc, less fizz. Even mostly clean lead alloys will fizz a tiny bit I find if you let the acid sit on it a while- But zinc makes it foam quick.
If you did really have zinc- If it wasn't thoroughly overheated- you can remelt your ingots slowly, keep the temp under 700 degrees. Once you get to 700 and everything is liquified, let the pot start to cool down. The lead will stay liquid, the zinc will try to solidify into a chunky oatmeal-like dross that will keep floating up to the top. It will look like partially solidified foamy grey stuff. You can skim it off the top of the pot. Hold your pot temp at this temperature (between 650-700) and stir and flux with a good hydrocarbon flux- parrafin wax (candles, crayons, etc), used motor oil, etc. and stir the alloy well making sure to scrape the sides and bottom of the pot to bring all the zinc to the surface. Then just skim it out until you have mirror-bright liquid lead in the pot, and recast your ingots.
A little zinc (1% or less well-alloyed) won't hurt your bullet casting alloy except to make it seem tin-starved and not want to fill out the mold. It also hardens the lead up a bit. More than that and you get a mess.
Thanks for the help!! I actually misunderstood you and did the process backward heating it up very slowly keeping the initial temp where the lead was the consistency of oatmeal. I didnt see anything happen there. When I warmed it up just to liquid I started fluxing like crazy. I did get the gray chunky content as you described. However, it kept coming up again and again as I fluxed. I realize that I may have put in a lot of zinc weights, but do I keep fluxing until I got nothing to the surface? I am assuming that when it stops then there is no zinc left in my alloy. My other question is how much of my other metals am I taking out, such as tin or antimony?
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