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George Babits
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identifying lead contiminants by color of melt
Jul 2nd, 2021 at 4:51pm
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Been doing some casting lately, mostly with scrap lead so I expect some contimination.   I get three basic different colors:  yellow (cadmium?);   blueish film almost like peacock copper;  and silver (uncontiminated).     The slag: earthy grey (tin? antimoney?), and brassy - - looks almost like fool's gold (Iron pyrite, calcopyrite, arsinopyrite).   Anybody have a clue?

George
  
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85lc
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Re: identifying lead contiminants by color of melt
Reply #1 - Jul 2nd, 2021 at 5:24pm
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Hmmm, how accurate are they?  You h=may have found the holy grail of bullets and also have pretty colored bullets.
  
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Schuetzendave
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Re: identifying lead contiminants by color of melt
Reply #2 - Jul 2nd, 2021 at 5:27pm
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Also aluminum and zinc floats to the top - not sure which color they produce.

I found the colors show if you let the pot get too hot and it melts these impurities which have a higher melting point.

Once the lead:tin alloy melts (much lower melting point) I scoop off the sludge made up of higher melting contaminants before it gets hot enough for them to melt - which then  gets rid of the color sheen on top of your alloy which seems to from when it gets hotter.

I have been using scrap lead for 25 years.
« Last Edit: Jul 3rd, 2021 at 3:30pm by Schuetzendave »  
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George Babits
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Re: identifying lead contiminants by color of melt
Reply #3 - Jul 2nd, 2021 at 6:13pm
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Yes, that's what I'm doing Schutzendave.   I have the temperature at about 800 degrees F.   Since, at this point I am casting Minie' bullets I really don't care if I take out the tin.  Hardness tests as pure lead.  I'm  just wondering what I am dealing with here.   It is mostly pure lead, but I tossed in a couple of pounds of soft junk to use it up.   

George
  
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Re: identifying lead contiminants by color of melt
Reply #4 - Jul 2nd, 2021 at 6:15pm
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What’s the scrap lead source and have a quessament of it’s hardness. Near pure lead at a high temp will produce a multi coloration 
And use more flux, the dross should only be gray ash
  
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Schuetzendave
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Re: identifying lead contiminants by color of melt
Reply #5 - Jul 2nd, 2021 at 8:18pm
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Melting Points:

Aluminum 1,221 F.
Antimony 1,167 F.
Brass 1,710 F.
Cadmium 610 F.
Copper 1,983 F.
Lead 621 F. 
20:1 Lead: Tin Alloy 574 to 597 F.
Tin 449 F.
Silver 1,763 F.
Zinc 787 F. 

Therefore I try to scoop the sludge off at 600 F. when I melt my 20:1 lead:tin alloy to cast bullets. (need to melt it at a hotter temperature to make the euteric alloy which later melts at a lower temperature)
If you scoop off at 800 F. some of the nasty impurities like zinc will be mixed into your alloy.

I do not use flux since they also enable some of the impurities to be mixed back into the alloy.

« Last Edit: Jul 5th, 2021 at 11:45pm by Schuetzendave »  
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Re: identifying lead contiminants by color of melt
Reply #6 - Jul 2nd, 2021 at 8:20pm
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Don't throw in old lead sewer lines. It stinks!
  
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Re: identifying lead contiminants by color of melt
Reply #7 - Jul 2nd, 2021 at 8:28pm
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Dave, that's only with pure metals. A lead tin antimony alloy melts at 365F to 482F for example.
  
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Schuetzendave
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Re: identifying lead contiminants by color of melt
Reply #8 - Jul 2nd, 2021 at 8:48pm
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It is difficult to get rid of the antimony with this technique so I try to find soft lead which you can scratch with your nail before I use the scrap lead - to try to eliminate or minimize the antimony in my alloy. Most of the other metals do not form a euteric alloy and can be removed at the 600 F.

« Last Edit: Jul 3rd, 2021 at 3:26pm by Schuetzendave »  
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George Babits
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Re: identifying lead contiminants by color of melt
Reply #9 - Jul 2nd, 2021 at 9:19pm
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Well, most of the lead was pure.   I also have some very soft "junk" that my hardness tester says is about the hardness of a 40 to 1 alloy.   I know that is the problem because the bulk of the mix was 99% lead from RotoMetals.  My pot was at about 800 as indicated by the Lyman thermometer.     The brassy dross is what makes me wonder.    Well, like I said before, it is more curiosity than anything else.   Thos big minie' bullets seem to want a hot alloy to fill out properly.

George
  
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Schuetzendave
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Re: identifying lead contiminants by color of melt
Reply #10 - Jul 2nd, 2021 at 9:28pm
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After I clean the dross off at 600 F. I take the heat up to 862 F. to cast my bullets.
  
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Joe_S
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Re: identifying lead contiminants by color of melt
Reply #11 - Jul 3rd, 2021 at 12:23pm
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scrap dealers have some kind of infrared pistol which will give you a readout as to what the content is. Not sure how accurate it is but if it works its amazing.
Joe S
  
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Re: identifying lead contiminants by color of melt
Reply #12 - Jul 3rd, 2021 at 2:59pm
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Joe_S wrote on Jul 3rd, 2021 at 12:23pm:
scrap dealers have some kind of infrared pistol which will give you a readout as to what the content is. Not sure how accurate it is but if it works its amazing.
Joe S


we have (at work) the xray  spectrometer - it measures the %ages of everything in the item.  That was my motivation to make one or two HUGE batches of what I had.  300 lbs of pure, 400 lbs of range scrap that I added a bunch of tin to - turned out 3% antimony, 8% tin and the rest lead.
  
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George Babits
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Re: identifying lead contiminants by color of melt
Reply #13 - Jul 3rd, 2021 at 3:55pm
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Access to an e-ray spectronometer would be awsome.   But, I don't want to go back to the university and start on a MS or PHD in geology.   Most assay shops use them in preference to fire assay.  But, when I was doing mineral exams 20+ years ago, it was about $125 a pop for an x-ray spectrograph of a sample.   It would be fun to take a sample of my dross to the geology department of a university.   The dusky grey with brassy specs, and peacock blue would drive all the PHD candidates nuts.

George
  
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Re: identifying lead contiminants by color of melt
Reply #14 - Jul 3rd, 2021 at 4:34pm
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I took some lead to a scrap dealer and they shot that magic pistol at some lead and showed me the results, no charge. Cozy up to your local scrap dealer and see if they will do it for you. 
Joe
  
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