Yellow/Gold Slag on Top of My Lead in Pot?


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JNewell
July 9, 2006, 04:53 PM
Puzzled...:confused:...assume someone can help...am very new to casting.

I melted some lead sheet scrap in my lead pot. As it got hot, an odd yellow/gold crust floated up on top. It looks almost like pyrite (fool's gold). It's a substantial volume of metal...seems to have a fair amount of lead still included, since it's pretty heavy. I did flux the pot. It doesn't want to stir back into the lead.

What is this stuff?

Can I/should I get it re-mixed back in with the lead? The bullets are destined for plinking in a Ruger Old Army so I am not very particular about hardness...just want something I can cast with and not to lose ~33% of the metal I start with.

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griz
July 9, 2006, 09:42 PM
I've seen a that nice gold color on the top of the metal, but only on the surface, never any volume to speak of. Wish I could tell you what it is, but I would be inclined to flux again and cast away.

calaverasslim
July 9, 2006, 10:44 PM
hey, maybe you found the famous secret, turning lead into gold.. Ya think? :D :D :D :D

RyanM
July 9, 2006, 11:05 PM
If it was actually gold, it would sink to the bottom, because gold is denser. Like mixing oil and water.

Chawbaccer
July 10, 2006, 12:09 AM
Tin oxide possibly
http://cavemanchemistry.com/oldcave/projects/smelt/13.big.jpg

Rottweiler
July 10, 2006, 09:40 AM
I've seen it on my lead pot too. I just skim it off, dump it in the empty mt. dew can that collects the dross and toss a pebble of wax in the pot to re-flux and continue casting. As far as I can tell it's just some sort of oxide. I do seem to see it more when the pot is rumming hotter than usual.

Grump
July 10, 2006, 01:55 PM
It's tin, the expensive part of your alloy, and critical to getting good "fill" on your bullets into the corners of the mold.

Stir and flux BEFORE skimming that dross off.

BTW, I thought lead was denser than gold. Gold melts at a higher temp anyway.

JNewell
July 10, 2006, 03:28 PM
Should I turn the temp down, or further up, to try to re-integrate the lead and tin???

RyanM
July 10, 2006, 03:49 PM
Nope. Lead is 11.34 grams per cm^3, while gold is 19.32 g/cm^3. In comparison, depleted uranium is like 19.07 g/cm^3 and tungsten is 19.3 g/cm^3. Gold is pretty dense and soft and would be an excellent bullet material choice, if it weren't so darn expensive.

Grump
July 10, 2006, 05:36 PM
Regulate your temp to your casting speed, if within reason. At your fastest clip, you should never have more than the faintest of frosting on the bullets, and you *should* wait long enough for the entire sprue to harden.

If you up your temp too much, you burn off your tin too fast.

If you drop it too low (or are too slow between pours and the mold starts to cool too much), you get bright shiny bullets with rounded corners. They don't shoot so accurate, especially at long range.

You using a ladle, or a bottom-pour furnace? Stirring is MOST important with the bottom-pours.

JNewell
July 11, 2006, 03:03 PM
Using a ladle.

I must have turned it up too hot melting the sheet scrap. It's going to be a project to get this stuff re-mixed, I think.

Grump
July 11, 2006, 04:39 PM
Seeing some of that yellow is normal, any time you have a decent amount of tin in your melt.

How's your hardness on bullets cast before you started stirring and fluxing?

Remember, the large surface area-to-volume ratio of anything other than ingots will result in relatively more surface oxidation getting into the mix when you melt it down.

If your alloy is still good, don't worry about it tin depletion yet.

If your bullets aren't frosted, don't worry about being too hot with your melt.

I strongly recommend the Handloader magazine Cast Bullet [whatevertitle] book. It will fill you in on a lot of tips not found in other books.

brickeyee
July 11, 2006, 11:56 PM
It is tin, the stuff that costs more than $4 a pound.
Keep the temp below 750F or so to limit seperation.

Dr.Doug
July 14, 2006, 02:07 PM
This is what I learned when I posed a similar question on another forum.

http://www.castboolits.gunloads.com/showthread.php?t=2700&highlight=gold+scum

Go pour youself a hot one!

Doug

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