Purple scum on my alloy

[robertbank]

The past month has been driving me nuts. I get gold, turning to blue/purple scum has been forming on the top of my alloy as the pot comes to casting temperature. I skim it off only to find the scum returns again slowly.

Any idea what cantamination I have going on here. Alloy is primarily WW.

Take Care

Bob

[Casting Timmy]

Sounds like it could just be from the temperature being too hot. If you need it that hot to cast well, turn down the heat and keep it in the golden color.

I have one mold that has to run almost to turning the top of the melt golden color.

[Charlie Sometimes]

I get that only when I melt "corroded" lead for muzzle loader balls, etc. Corroded lead is processed to nearly pure, IIRC. Seems to me to be dirt and oxides left over from sitting too long, but could be the 1% that ain't pure. I find it goes away when I add a very small percentage of tin to help lessen the surface tension and improve castability in maxi-balls, etc.

Not sure if this was helpful, but best I can do not being a chemical engineer. :smile:

[felix]

Charlie has it about right. The metal you have is made with almost all lead. Proof: Pour out a pound brick, wait for a week or two and then drop it on concrete. If it goes "thud" with little or no ring, then guesstimation is correct. Anyway, add tin until the color goes to normal in the pot, but not over 3 percent of what is in the pot, pound wise, because it would be waste of tin for the effect you are after in the gun. ... felix

[fryboy]

there used to be a stikki ( i thought ) entitled , purple and gold oh my , or something like that , leaving me to believe yo have the good stuff

[Charlie Sometimes]

I should have clarified that, felix. I didn't mention percentages, because when it is melted in my pot, I take 50/50 solder (60/40 or similar) and melt it in a little at a time until the discoloration disappears, and then I stop. Hope that give a better idea of what I do.

[lwknight]

Robert , do you have a thermometer?
If you are getting the melt to 800 degrees then you should expect wild colors.
Thats too hot anyway.
Adding 1% of tin will allow you to cast at a much lower temperature and not add enough hardness to matter.

[bumpo628]

Here's the sticky:
http://castboolits.gunloads.com/showthread.php?t=63550

[robertbank]

Thanks guys turning down the pot works for me and I can add some tin as well.

Take care

Bob

[JIMinPHX]

I think that
gold = tin
blue = lead
purple may be manganese

[robertbank]

Turning down the pots heat setting worked! Thanks guys . Now to reclaim al the "scum" I have been skimming off.

Take Care

Bob

[tinsnips]

Years ago i use to pour lead joints [cast sewer pipe ] if the lead got to hot it turns all kinds of colors. It was pure plumbers lead .

[Fire_stick]

I have some ingots made from lead sheetrock backing. They have a purple tint. I call them "purple haze" lead. Very soft. I thought I remembered reading somewhere that this was a sign of nearly pure lead.

29502

[4719dave]

Funny,I have ths same caved in muffin ingots I got 2 coffie cans from this old plumber ,he told me if i could pick it up with one hand i could have it for free .well its all melted now !!!!!!! I watched the heat !!!! it seem to melt faster then the roof boots and would freeze up as fast also purlpe haze

[robertbank]

I scored 165lbs of isotope bottles from the local hospital today. I understand they are close to WW in alloy content. I also got quite a bit of lead sheeting from them as well. It is from isotope containers I suspect. It seems rather soft as the ingots land with a thud as opposed to a slight ring from the ingots cast from the bottles. Is this close to be correct? I intend to mix the two types and add some tin via 50 50 solder ingots.

Take Care

Bob

[Cowboy T]

Since I use aluminum moulds, I tend to run my pot hot, about 700-800 degrees, depending on the specific mould. If you're above 600 degrees, you'll get that purple/blue/gold haze (I see it at 650 during initial wheel weight meltdown). That's oxidation. Just keep casting, flux occasionally, and don't worry about it.

[lwknight]

I have some ingots made from lead sheetrock backing. They have a purple tint. I call them "purple haze" lead. Very soft. I thought I remembered reading somewhere that this was a sign of nearly pure lead.

29502


That is sooo pretty snif snif.

[Reg]

You are just running a bit too hot is all. Really not a problem. Bet when you flux it goes away for a bit. Get a thermometer and check your temps.
Good idea is keep a few old-junk- whatever lubed bullets on hand and use them for fluxing say, every fifty heads or so. Will even out your alloy and help hold the temp more even. Do run with a thermometer however. Just like buying a cheap cronograph, it will be a learning experiance and teach you a bunch.

:drinks:

[9.3X62AL]

I've only encountered the purple and gold highlights at the top of the melt when using pure or near-pure lead. I do tend to heat unalloyed lead up fairly high to make it run well, flux it, and make RBs or Minies.

[bumpo628]

Here's the best deal on a thermometer I could find:
Tel-Tru LT225R, 5” stem, 200/1000F (manufacturer of the Lyman model)
$25 delivered and it only takes 3 or 4 days

search the page for their part no. "BBQ250-5-1000-cl"
http://www.kck.com/tel-tru_grill_smoker_thermometer.html