Gold and purple and blue... Oh My!

[ilcop22]

So a while back I bought 70# of lead. This was an unfortunate e-bay purchase. The seller marketed the lead as "Wheel weights. Fluxed. Dirty work is done for you."

It came in lyman 1# ingots and 1/2# pan ingots. The lyman ingots were as clean as expected. The pan ingots, however... They tell a different story. I'm hoping someone can help me identify the garbage in these ingots.

The melt forms a gold hue on top which, for the life of me, I can't clear up. After fluxing, the surface becomes a deep purple color. Tonight on the second flux, the surface turned dark blue. After I cleared that out, the gold returned. Despite several attempts (and a lot of time) flux/skimming doesn't clear it out.

Any idea what this crap is in the lead? I'm able to pour fairly decent ingots as my RCBS ladle doesn't let much of the gold stuff through. Fluxing of the poured ingots clears everything out.

Any help is appreciated. I'm getting close to just reselling this stuff to someone else.

Thanks!

[tommag]

Pure lead gets a purplish look to it when it is heated enough, and I think I recall a gold stage, as well, although I am not sure about that.

[waksupi]

That is tin oxide you are skimming off. Flux it back in.

[docone31]

That is for sure.
It soulds like you got the Grail.

[ilcop22]

Good thing I don't throw out my dross!

The gold colored lead is tin oxide?

[docone31]

Purple, or Blueish is pure lead.
The brown, or golden hue is tin. Lots of time, when I melt my roof boots, I get a full pot that looks Golden. It is the tin some use on the joinery of the boots.
It soulds like you hit the Grail with that purchase.

[sagacious]

Good thing I don't throw out my dross!

The gold colored lead is tin oxide?

No, not tin oxide. Neither SnO nor SnO2 are yellow.

The main problem that caused the colors has not yet been addressed. The cause of the colored dross is excessive heat. The melt was overheated.

When lead is heated far past it's melting point, it begins to oxidize. The thickness of the oxide layer determines the color. It is exactly the same as the yellow/orange/blue/purple oil or gasoline sheen on water-- the thickness of the oil layer determines the color reflected back at the viewer. If you watch the overheated lead, the color of the dross will slowly change and ultimately become purplish and then black. The chemical composition hasn't changed, but the thickness of the layer is increasing, and thus the gradual color change.

It would sure save a lot of time if one could overheat their melt and simply observe the resulting oxide colors and thereby divine the composition of the mix. Unfortunately, that doesn't work as well as one might hope. However, the following holds generally true:
"Pure" or relatively pure lead is most prone to forming a colorful oxide dross.
Lead alloys containing much tin will usually "sweat" shiny tin droplets or beads during heating and shortly before melting. This is often diagnostic when higher tin content is suspected in a lead alloy.

The reason the colorful dross couldn't be "removed" by fluxing, is because it's the lead itself that is forming those colors, and you can flux until the lead is all gone, but that dross will keep forming if the melt is too hot. The colors are NOT formed by impurities, contaminants, or crud.

Reduce the temp of your melt next time, flux, and you'll have a pot full of shiny lead. More heat is not always the answer. If you generously flux your saved dross at a lower heat, you can probably recover some lead.

Hope this helps, good luck!

[runfiverun]

hue was the clue there.
tin forms a gold layer that isn't so tranparent.if you get blue or purple in a tin alloy run away.

[sagacious]

hue was the clue there.
tin forms a gold layer that isn't so tranparent.if you get blue or purple in a tin alloy run away.

The yellow oxide dross is not diagnostic for tin content.

"Chemical lead" with no tin in it will form that yellow, then blue, then purple oxide dross. The lead does that on its own.

[runfiverun]

it's a totally different colorer not color,maybe but depth might be a better description.

[sagacious]

Tin will oxidize readily and quickly when overheated, and since the first color to appear is gold, many people naturally assume that the initial dross coloration is caused by tin, and the later blue and purple colors are lead. This is not the case.

The color sequence is due to the molecular thickness of the oxidation layer, and the colors themselves are produced by the interference of light reflecting off the top of the oxide layer and also the top of the molten lead, and interfering. Eventually the oxide layer gets too thick for light to penetrate and reflect off the molten lead underneath, and the dross turns from purple to black.

The colors one sees on an overheated pot of lead alloy are caused by the oxidation of the lead itself, and the color is not diagnostic of tin content at all. It's the same thing as the iridescent colors produced by soap bubbles, or gasoline on water.

As Paul Harvey would say, and know you know the rest of the story.

[ilcop22]

On sagacious' points, the lead mix was actually at my normal melting temp. In the same pot on the same heat settings I melted other tin mixed alloy with no issues. The solid lead itself has streaks of purple and gold hue to it before I even melt it. Its only when I melt the pan ingots that I get these color issues. Overheating the mix is not the issue.

[swheeler]

Sounds like pure lead to me, I still have ingots smelted years ago with the blue streaks in them. When I cast minnie balls I see the yellow/blue/purple hues form on top the melt, just keep casting bullets come out fine. Test an ingot for hardness, I'll bet it is real soft stuff close to a 5.

[madcaster]

From the title of your thread i thought you had a wreck on a motorcyce or something-glad you are okay!

[9.3X62AL]

Interesting texts, Sagacious. I've seen these same hues in unalloyed lead, and not in lead/tin or lead/tin/antimony alloys. So, I think your observations have merit. There sure wouldn't be any harm in backing the heat down a bit to see if that metal DIDN'T go "60's Light Show" on a caster.

There can be some genuine "mystery metal" out there, IlCop. Without an assay, it's hard to know exactly what you're working with. It may indeed be unalloyed lead, and the Light Show might be an indication of same. Hard to say. Unalloyed lead ingots usually don't give the ringing sound when dropped on concrete that alloyed lead (with tin or tin/antimony) produces. Not real scientific, but boolit casting isn't always rocket science--which is a good thing, in my case.

[ilcop22]

Madcatser - Thanks for the concern! I was going for a "Wizard of Oz" pun.

9.3X62AL - I've done some heat adjustments with the stuff in the past. I'm gonna take all the advice received (starting with dropping it on the floor lol) and see how things work out. The lyman ingots I fluxed do make that lovely ping sound as I deliberately dropped the finished ingot I made on the ground.

[runfiverun]

you can tell my way with words is very clear at times, knew what i wanted to explain just couldn't get the correct terms going.
sagacious done a far better job than i could.
and is fully correct.

[sqlbullet]

normal melting temp

If the tin content is high, then your normal melting temp may be high as well. Melting points drop to almost half as tin content rises.

[ilcop22]

I intend on trying all suggestions, including further tweaking the melt temperature. I'll let ya'll know the result!

[sagacious]

If the tin content is high, then your normal melting temp may be high as well. Melting points drop to almost half as tin content rises.

This is a very important observation. As the alloy changes, the heat that it should be kept at may change dramatically. One cannot have a "standard" melting temp for all lead alloys.