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Thread: Help with identifying zinc

  1. #1
    Boolit Master The Real Doc Holliday's Avatar
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    Help with identifying zinc

    Its been a very long time since I have been on here or even thinking about casting but now I want to go at it again but have an issue. I know I had between 300 to 400 lbs of contaminated lead that I bought from a guy on ebay (never trust people on ebay that say they know about not melting zinc weights into the mix)

    My kids wanted to move the lead that I have in their garage to the other side without having me there to help or oversee... I have health issues and they were looking out for me. Well they mixed the contaminated lead in with my 1200lbs of known good lead (WW lead alloy that I melted myself). I wanted to separate it so I got some muraitic acid and started putting a couple drops on the lead after scraping it to get rid of the oxide and everything bubbled.

    I then put drops on my pewter and boy does that bubble!!!! so my question is..... does muraitic acid react to Tin? my pewter should not be contaminated but it was eating it away.

    Any help is appreciated

    Doc

  2. #2
    Boolit Master The Real Doc Holliday's Avatar
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    I guess my title could have been more informative of what I was saying : (

  3. #3
    Boolit Master
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    My pure tin and pewter do not bubble at all. AAMOF! I use muriatic acid to test dubious pewter items. My ingots, nuggets and pewter are not tarnished, though I suppose under the right conditions oxides could form. I do not know if oxides of tin would bubble with HCl.

  4. #4
    “Muriatic” acid is a slang term for hydrochloric acid, or a solution of water and HCl. The specific strength of acid we use in the pool industry is 31.45% HCl. Pound out a thin strip of solder 95/5 or Pewter 92 to 95% Tin. put tin in test tube with an oz or two of Muriatic acid the mild stuff used for concrete/pool cleaning will dissolve the tin strip. This common gold testing solution is also know as "Stannous chloride".
    Last edited by unclemikeinct; 02-18-2020 at 10:41 PM.

  5. #5
    Boolit Master
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    How long does it take to dissolve the tin? I've left pool acid on the surface of pewter for ten or fifteen minutes and all that happened was a very slight color change. No bubbling, pitting or dissolving that I could see, as opposed to zinc items that with the same drop would look like it was boiling as soon as it touched the surface.
    Last edited by kevin c; 02-18-2020 at 11:27 PM.

  6. #6
    At room temp you can see the fizzing right away. A one inch size piece of 95/5 solder pounded flat. Is really chewed up in less than an hour.

  7. #7
    Boolit Master
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    Wow, you're right!

    I took a strip of touch marked pewter and suspended it in a little jar of muriatic acid (pool acid - my bottle was marked something like 32 1/2% HCl. Btw, I thank you for encouraging the experiment; the old plastic bottle was beginning to blister on the bottom, resulting in a careful transfer of the acid into glass). It sat for a minute or so, then start to fizz. The fizzing kept up all the time I watched over fifteen minutes, then I left. When I came back the part of the strip in the acid was gone, and the rest blackened. The acid had a fine black particulate in the bottom (the copper and antimony in the pewter?)

    This fizzing was a lot milder and delayed compared to what I see with zinc, which is what I'm looking for when I test pewter.

    Curious, I put drops of the same acid (not a soak like above, but much more than what I test with) on the same pewter item I cut the strip from. I also did the same HCl application to two pure nuggets of tin. No immediate fizzing, just the very slow formation of a few small bubbles. I left it for the same time as the strip and came back to find the acid evaporated, the pewter surface etched to the point that the touch mark where I applied the drop was gone, and the tin nuggets looking slightly discolored and maybe a bit roughened.

    Perhaps the passivation on the pewter delayed the reaction, and the small amount of acid in the drops I usually apply aren't enough to produce much gas (hydrogen, right?). I think looking for an immediate strong reaction still points to zinc, but now I know gas production can be seen with tin as well.

  8. #8
    Boolit Master The Real Doc Holliday's Avatar
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    Unclemikeinct, thanks for the great info... I guess I will have to melt all of my lead allot and mix it together to make sure the % of zinc is minimal. I really wasn't looking forward to putting acid drops on 800 2lb ingots ��

    Doc

  9. #9
    You have to find a way to sort those ingots: w/o re=melting them Doc. That is just too much work. Try a drill bit at least a 1/4 inch, quick pop on the surface. Just a small divot. one drop of acid. You may be able to figure from intensity or the color. Zinc From Tin alloys.. Good luck, unclemikeinct oh yeah, then sell the bad ingots at the scrap yard.
    Last edited by unclemikeinct; 02-20-2020 at 07:47 PM.

  10. #10
    Boolit Grand Master

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    I'm sorry that your lead got mixed up but its hard to fault good intentions. This kind of stuff makes a good argument in favor of permanently marking your ingots. I have only recently started doing this. I wish all of mine were marked.

  11. #11
    Hey Doc, one other thought on those contaminated ingots. Zinc only weights 6.83 grams for a C/C. Tin is 7.265 grams per c/c cubic centimeter. If those ingots are similar size, the zinc contaminated ones will weigh less. Maybe that can help you confirm the good alloys from the bad ones. unclemikeinct To take that idea to an extreme. you could weigh them by displacement of water per c/c..
    Last edited by unclemikeinct; 02-20-2020 at 11:30 PM.

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