Woe and Intrigue: Thick Brown Dross

[Woodsroad]

So, it's a nice day and I decide to smelt the soft lead sheet, pipe and ingots from the scrap yard.

I almost fill the large cast iron dutch oven with melt. There is not a lot
of dross, but what is there is a very fine, dark, heavy powder, difficult to
remove, even after fluxing with Borax and then beeswax. Clearly, there is
lead intertwined with this stuff. I manage to remove it all.

I cast six muffin tins of ingots, they look good, and decide to add more lead to the melt. After the pot is about half full, one leg of the burner begins to rapidly sink into the dirt. I guess the dirt under the burner had melted and that leg was sitting on ash or something. I manage to remove the kettle from the burner, but, in doing so spill a good bit of melt on the dirt. I wasn't hurt, I had on thick boots
and pants and gaiters. I get the kettle on blocks and continue with the melt.

After I get the melt back to around 650ºf, I peel the lead off of the dirt and add it back to the melt. There is a lot of crap stuck to it, since I melt next the
burn pile. I continue adding sheet lead, removing the fine, heavy powder as
I go. One extra thick sheet, marked "low level radiation shielding" takes a particularly long time to dissolve, and some of the thin sheet seems to float a little, but does melt. I assume that the really thin stuff has a heavy coating of oxidation.
I flux again and begin seeing a pretty weird thing: Brown/red/green dross "bloom" starts rising out of the melt. I remove it. It is very heavy, with a consistency of dirt. Molten lead can be seen trapped in it. the melt temp is now at 780ºf, and I turn off the burner.

As I remove it, more rises to the surface. It's looks like that this is an oxide, forming as the surface of the melt is exposed. I realize that I could sit there and remove it all day. It looks like rusty dirt, but is not magnetic. If I scoop some
up with a strainer, as the molten lead drips out of it, it leaves a
stalactite of slag, which begins to glow and burn off, giving off a thick
yellow smoke. I do have a respirator on.

What the &^%$# is happening here?

I cover the pot and turned off the heat. I wash all my clothes and throw out the gloves that had on.

Any ideas?

Thanks!

[44man]

Most is just that---dirt, along with old oxidation. I don't use a slotted spoon, just a plain spoon to work the crap to an edge to skim off. You need to stir it good with flux to get all the trapped junk to the surface. No need to worry as long as it comes out clean in the end.

[zxcvbob]

I wonder if the "low level radiation shielding" was zinc instead of lead? (zinc should be good enough to stop alpha or beta particles; not sure about low-energy x-rays)

[Woodsroad]

It's an awful lot of dross. It keeps forming and it's heavy. I'll try using a regular spoon to scoop it out and see what happens...

[Woodsroad]

I wonder if the "low level radiation shielding" was zinc instead of lead? (zinc should be good enough to stop alpha or beta particles; not sure about low-energy x-rays)

It was too soft to be Zn. An alloy, perhaps....but it was soft.

[zxcvbob]

Good. Try fluxing with a little Crisco or lard at high temperature. It will turn some of that heavy dust back into lead. Don't know what to tell you about the glowing smoky stuff.

[Woodsroad]

Good. Try fluxing with a little Crisco or lard at high temperature. It will turn some of that heavy dust back into lead. Don't know what to tell you about the glowing smoky stuff.

OK, I'll try lard or Crisco. Isn't Crisco hydrogenated canola oil? I also have a lot of beeswax (I keep bees, too). What will Crisco do that borax or beeswax will not?

The bloom of dross started after the last flux with borax, I was stirring it in really well, scraping the bottom of the pot as I stirred. I had skimmed off all the usual dross, the top was nice and shiny, I turn back to the kettle and there is this stuff, rising up and accumulating.....giving off a yellow smoke as I skimmed it. Strange brew, indeed.

[odoh]

I read w/interest your comments re the very fine heavy dirt. I too have been experiencing same stuff w/lead pipe/roofing jacks etc. Not so much w/WWs but some. The stuff sticks on the sides, bottom of the pot and even the dipper. Haven't seen it mentioned before now ~ but then I'm new to this.

As for the wierd stuff, I'd treat it like I treat the fine dirt and other dross. Save it and then re-smelt it later to extract what lead I can get out of it before dumping the dirt. I have had good result using pat martins sawdust/shavings. Today, for the first time I used some old borax found when cleaning up the garage to resmelt the save dross w/good results. Keep us posted how it goes ~

[zxcvbob]

I haven't tried beeswax cuz I don't have any bees, so I can't compare it.

Shortening or fat is the best thing I've found for fluxing. Not sure why, but I think it's because the glycerin takes a while to burn off after the fatty-acids are gone -- so after the initial smoke and/or flame, there's a bubbling charred liquid left that's easy to skim (or stir down and let it burn some more.) Old motor oil or paraffin candle stubs burn up too quickly.

[Woodsroad]

I read w/interest your comments re the very fine heavy dirt. I too have been experiencing same stuff w/lead pipe/roofing jacks etc. ...Keep us posted how it goes ~

Yeah, this was roof flashing, Pb pipe, cable jacketing, foundry ingots without any numbers (seemed soft), radiation shielding and sheet lead of unknown origin, all soft.

I smelt in a 20 qt dutch oven, and I guess that it was a little more than half full of melt. From that, I filled a 2 gallon pail 3/4 full with dross.

I'll give it a remelt on Monday and keep the heat lower. Maybe make some pics, too.

[Woodsroad]

...Shortening or fat is the best thing I've found for fluxing. .

Well, we have a tub of it aging in the back of the fridge, I'll give it a try and report back! Thanks.

[Crass Whackwords]

It has been my experience that the drive-you-crazy oxidation is normal with pure lead and or nearly pure lead.

I thought maybe it was some kind of contamination so I bought some foundry grade pure lead and it drosses like crazy, too.

Normally I prefer to cast with a ladle but for these drossy alloys a decent bottom pour pot would be the way to go. Put sawdust/charcoal/what-have-you on top to minimize the dross and cover the pot. Let it dross and don't worry about it because the dross is on top.

If you cast with a ladle, the dross keeps plugging up the ladle and results in lots of cussing. Then you have to flux frequently which smokes and smells and results in more cussing.

If you are casting for blackpowder, I guess you have to deal with this dross problem, but for smokeless loads use clip-on wheelweight and life is so much easier.

[Woodsroad]

I've been told that I was running the melt too hot. Keep it around 650º. I always watch the temp when smelting WW, but I figured, what the hell, there's no zinc in this stuff, no need to watch the temp to closely...well it seems that pure lead forms lead oxide at higher temps. I have some alchemy experimenting to do now to see if the dross will return to solution. I think not. lesson learned....

[docone31]

I collect my dross. After I have done my prime smelting, I save the dross for the last pot of melt. I toss it in with lots of charcoal. In time, the charcoal breaks down, and so does the dross. Most goes back in the melt.
When I melt clips off, or batch my melt, I do not keep scrapeing the dross out. If I did that, I would have nothing but oxides.
If you leave some on the top, nothing takes its place.

[Woodsroad]

OK, I will try the charcoal route.

Understand, I am not talking about a little dross. I'm talking about 2" of dross.

[Crass Whackwords]

2" ??? Wow, that is a lot. I'm used to seeing 1/4" with pure lead, and 1/4" is bad enough.

Are you saying that after you clean off the 2" of dross, another 2" soon appears ?

Post a picture if you can.

Normally sheathing and flashing is lead with a wee bit of antimony, similar to stick-on WW, but there are other possible additives that are not bullet-casting friendly.

[Tom Herman]

I wonder if the "low level radiation shielding" was zinc instead of lead? (zinc should be good enough to stop alpha or beta particles; not sure about low-energy x-rays)

You need elements a lot heavier than Zink to make effective shielding against gamma radiation. Zink is only atomic number 30... You need to be much higher (like Bismuth at 83) to be effective at stopping gammas...
Yes, almost anything will stop alphas or betas. Alphas are essentially a Helium nucleus, and are stopped by thin barriers such as a piece of paper or two.
Betas are free electrons and are stopped by slightly thicker material, such as a layer of skin (beta burns), or fairly thin, heavy metal.
Gamma particles or energy fragments penetrate deeply, but fortunately don't have much energy. It take a lot of material (the denser the better) to stop it, the higher Z materials work best.

Happy Shootin'! -Tom

[runfiverun]

i am thinking that bismuth might be your culprit here.
you might want to try adding a bit of tin to your melt and see if that helps.
just a small batch and 50-1 might help.

[powderburnerr]

I make 16 pound ingots when i do soft lead and it sets outside til I use it . when I melt it back down I ocassionally get a clump of the stuff in one of the ingots ,I do not see it when I pour them but find them on the remelt . It doesnt seem to effect aanything I just scoop it out when it floats up .and it seems to disolve when i resmelt ..might just be some lead or oxides of lead that is not fully breaking away from the melted lead would be my guess..........Dean

[stocker]

How big is that "large" Dutch oven? ie: what is the diameter? I'm wondering if you have so much surface heat loss that you are getting a large slush layer and the normal dross is bound in it. If so the answer might be more heat or a narrower pot to reduce top surface area.