Skimming Slag

[Nav]

I’ll preface this with saying I’m new to casting and I’m still learning. Despite this, by following the directions I’ve been able to produce very uniform balls with the Lee two cavities and pot. I talked the manager of a local, industrial lead distributor into selling me some giant ingots for cash. He said they were 99% pure. When I melt them down the only “slag” I’m getting is a golden skin that seems to accumulate steadily on the surface as I’m casting. I don’t think it’s “slag” in the sense that it does not look at all like what I’ve seen watching YouTube’s of people casting. It’s very uniform and constant. It’s easy to skim off, but it doesn’t look like what people using wheel weights or old lead are removing. Does anyone know what this is?

 

[Phil Coffins]

It maybe your temperature is too high and that is oxidizing lead.

 

[Rifleman1776]

That coloration is from the small amount of non-lead impurities in your pot. You should skim them off regularly. I still to raise real slag and the impurities then skim with a large old spoon.

 

[Nav]

This is what it looks like cold.

I’ve been skimming it. I’m just not convinced it’s “slag”.

 

[64Springer]

Oxidation.

Push it aside and keep pouring.

If that's a bottom pour pot, there's no need to skim.

Skimming is only required when using a pouring ladle. And even then, the oxidation floats to the top. Leaving clean lead in the bottom of the ladle.

 

[Nav]

I’ve got it on 6 when in ready to cast. Should I go cooler? Not that this is much or it really matters. I just kind of wanted to cheat and use the purest lead I could.

 

[64Springer]

725 to 750 is a good pouring temp.

Lee makes a lead thermometer.

Invaluable when casting.

 

[andy52]

honestly other than a serious slag buildup all of it floats on top and you're drawing from the bottom, so unless your pot gets really low there's no worries.

 

[Nav]

I would think there is oxidation at any temp if it’s in a liquid state? It still forms that skin right up to when it resolidifies.

 

[The Crisco Kid]

I read somewhere that a layer of charcoal on top will prevent the formation. I never tried it since I just scrape the stuff off occasionally.

Lead thermometers are not always accurate. I had one that read a 100 degrees low. I thought my pot was not working until I checked the thermometer against two others. 800 degrees read 700 on the new but defective one.

 

[ZUG]

Just flux the pot and stir once in a while and continue to cast. I would not skim off this stuff -- Your lead is very clean and very pure - good stuff you have there

 

[Phil Coffins]

Yep, that just normal oxidation. Nothing to deal with just cast away.

 

[smo]

As the pot gets lower the lead gets hotter…

The pot looks low& too hot too me..

 

[bronko220002]

Keep your temp between 700-750 and with your bottom pour pot just keep casting. No need to skim off that. I only skim heavy slag off my bottom pour.
Skimming is mostly reserved for those casting by dipping with a ladle and hand pouring.

 

[1950DAVE]

Frequent skimming will only lead to more oxidation, as fresh metal is exposed to the atmosphere.

 

[Justin.44]

I’ve got it on 6 when in ready to cast. Should I go cooler? Not that this is much or it really matters. I just kind of wanted to cheat and use the purest lead I could.

As the others have said, it's fine and your lead is good. In my experience, pure or nearly pure lead will get a variety of colors on the surface if heated too much and will go through a wild rainbow of gold, blue, purple, etc.. When I melt stuff that has much tin or antimony I don't get those colors at all.

I saw this thread before I went out to make some ingots and remembered it when I was getting done so I left a little in the bottom of the pot and kept the heat up and snapped these pics as it changed colors. You can see in the first pic some of it's blue and some is the gold color you mentioned and in the next pic the gold had turned blue.

 

[necchi]

Does anyone know what this is?

Another vote for it's just the heat. If there's nothing to skim,, just stir. Your good, keep the rhythm when casting esp with those Lee's, lube the pins on the those blocks and don't "knock" too hard

 

[BillyC]

I read somewhere that a layer of charcoal on top will prevent the formation. I never tried it since I just scrape the stuff off occasionally.

Lead thermometers are not always accurate. I had one that read a 100 degrees low. I thought my pot was not working until I checked the thermometer against two others. 800 degrees read 700 on the new but defective one.

If it was a mercury thermometer check for a break (air pocket) in the mercury. If there is one cool it down very low, like with dry ice and suck all the mercury into the bulb and then let slowly reach ambient temperature and the break (air pocket) will be gone.

 

[nhmoose]

Oxide colors, great pics shown Justin44

 

[bronko220002]

Nav, don't go by the numbers on your pot. They are only a reference. Buy yourself a casting thermometer. They're not very expensive but well worth it. I normally cast right around 700*-750*