What is causing this color in my pot?

[rosewood]

I have seen this before and seem like it caused casting problems. Kept clogging up my bottom pour spout. The purple and blue in this seems to make the alloy less pourable.

Any ideas? Is there some way to get it out? This is made from wheel weights and typically, the mix is shiny when melted and just dull gray when cooled.

Thanks,

Rosewood

[OS OK]

I get that color when I'm working with soft blends of roof flanges & adding Sn for HP's...I flux it back in but I still get the rainbow of colors on top.
Looks like you have a lot of Sb on top too...are you keeping the pot fluxed well? @ 700*F. all that extra Sb will flux back in the blend.
Also stop pouring when you get to 1/4" ~ 3/8's" or so of Pb in the pot...when you start a new batch all this will come to the top and stay away from your spout.

[rosewood]

So, that is tin that was gray and clumping on the top? I was wondering, it just didn't seem to melt down like I thought it should. Usually, it looks like a mirror on the top after I scoop off the junk, but it didn't this time. I flux with candle wax and had done it several times. Kept stirring also, but can't remember the mix looking quite like this. This isn't my casting pot, it is my smelting pot (plumbers furnace), I was making ingots with this batch.

Rosewood

[OS OK]

Wax (the size of a butter bean) is fine in the pour pot to keep air away but in the smelt pot use saw dust...lotz of it, lotz! It will charcoal.
No...I don't think it's tin (Sn), I think it is antimony (Sb), saw dust forms a more thick barrier on the pot keeping the oxygen away from the melt which forms the dull grey and thin layer. Generally when the melt is just coming to be melted the antimony will come to the top and look like a 'slurry', some mistake it for zinc (Zn) but generally is not. If Zn were there it'd look like oatmeal got stirred in.

[rosewood]

Err, i knew Sb was antimony, had a cranial air explusion.

Thanks for the info.

[rosewood]

You have me wondering now whether it is zinc or antimony. Some of it did look like oatmeal, or at least grainy. I have a lot that I skimmed off and put to the side. I thought I culled out any weights that were zinc, but possible I could have missed some. I don't get the pot too hot, usually run about 700 so zinc should have not melted. If I have extra antimony in there, I wonder where it come from. Everything in the pot was clip on wheel weights. Hmm..

[marek313]

My guess its a combination of Sn / Sb as it this pot doesnt look like it was fluxed enough. I usually flux well when I smelt and only flux once in my casting pot if I really need to. When I cast my pot will go all the way down without leaving any alloy on the sides. When I'm down to the last pound or so I just put little piece of wood under the stand to tilt it a little bit and I get nice half circle ingot out of the remaining alloy. When you get that low there will be some Sn / Sb on the surface along with some dross. Those ingots go back to the smelting pot and get at least triple fluxed to get everything back in the alloy.
As for the color its probably because your pot is empty and it was too hot when you shot it off. Every time alloy starts changing colors whether its blue, purple etc its because your alloy is too hot.
If this is unusual for you then there might be a chance of some zinc being in there. Muriatic acid would be good to test for zinc.

[OS OK]

Generally clip-on wheel weights are 3% Sb...it should be there.
If you had Zn in the pot, it would have taken a lot of those to leave that much on top after you have been skimming.
Something about the pour pot I should mention, save the oxidized Pb, Sb & Sn that your skimming and run it again when you run ingots...it'll stir into the new metal. I dump my skimmings in a little tin pot and save them till theres 1/2 pot full then re-run them into ingots.

[masscaster]

I don't think it's Zinc either. That is a heat color, and not from anything bad in the alloy.
Try running the alloy cooler when you render, keep stirring and stirring. When you get the impurities into a mass on top flux it, with more stirring and stirring.
You'll know Zinc when you get it bad.

Jeff

[rosewood]

I am pretty sure I kept it about 700 degrees or under. I keep a thermometer in it when making ingots. Same way I always do it, but this is the 2nd time ever I have had the color issues. I even see it on the top of the pot, not just when it gets low.

Reckon I should take the ingots I made and reheat and mix it all together again and repour? Could my Sn/Sb not be mixed in well enough?

Thanks,

Rosewood

[rosewood]

As for the saw dust. Should I just cut a 2x4 with the circular saw and catch the dust since I don't have any handy? Then do I sprinkle it to cover the entire top of the melt?

Thanks,

Rosewood

[lightman]

The color looks like what you see with soft lead. The other stuff should flux back into your mix. I don't think its zinc.

[OS OK]

Your Sn & Sb is in your ingots and is mixed well...those contents have only been reduced by the amount you have skimmed. Prolly doesn't matter but if you decide to do that you'll need a couple of cups full of saw dust to do a two or three flux batch. Remember it needs to be thick enough to completely block any metal from the air.
Only you can judge this but, if it were me I'd just save it for the next ingot batch.
You should be able to get sawdust for free from a box outlet like Home Depot, wish you were near me I keep a huge amount in my spare 40 gallon trash can.
I put a full cup full into the bottom of the pot as I start to melt the Pb, this way the Pb is covered throughout the entire melting process, then stir, stir, stir...pull the burned up sawdust off the top and quickly ladle my muffin tins full of fresh Pb.

[OS OK]

Found it...this is the picture I wanted to show you...there's 35 lbs. of melt under this saw dust and the saw dust is prolly 1" thick after its burned.
In this state here is when I stir like heck, carefully scraping the sides and bottom of the pot to loosen and send all the dross to the top, then I take it off and start ladling in the picture above.

When you pull the dross off the top of this pot it's beautiful silver metal below.

I made a scraper tool that fits the bottom angle of the pot so I get all the dross off the corner at the bottom all the way around.
Some scrape with a wood stick, ie. a paint stirring stick BUT...if using wood to stir and scrape make dang sure it's a fully dried piece of wood!

[rosewood]

I bought a $1 metal slotted spoon from the dollar store and put myself a wooden handle on it to keep cool. It works great at getting the dross off the top.

Most of my batches have been just as you said, shiny metal after removing the dross and I only used wax for fluxing. Been only 2 occasions where it was not and it has made me think there was some sort of contaminant.

Thanks again.

[dondiego]

Sounds like you might be rendering wheel weights in your casting pot. That is a good way to get crud in your spout.

[bangerjim]

It is called .........PURE LEAD! It turns reeeeeeel perrrrrrdy colors of the rainbow as it heats/overheats up. Don't loose any sleep over it. it is perrrrrrrrrrrfectly normal.

Add some Sn/Sb to alloy up to 10-12 hardness for what we mostly use.

[dondiego]

He said that he only used wheel weights in this pot. I thought it was pure lead too from the appearance. Must be close to it.

[USSR]

The color looks like what you see with soft lead.

+1. Nothing to worry about.

Don

[rosewood]

U guys may be on to something. Maybe the Sn and Sb were not mixed in well and I scooped it off with the slag and left near pure lead. I think I need to flux more.