Question about black scum on top of alloy

[seabreeze133]

Restarted casting after a layoff and have a strange to me issue. Black scum (don't know what else to call it) forms on the alloy. I can get it off by fluxing and about 2 casts later it reappears. Looks as if I have about 15 Lyman ingots that are in trouble. Only thing new I can think of is I bought a candle to flux with. But in a previous life, candles are all I used.

This is WW maybe 15, 18 years old.

Any suggestions on what I have done?

thanks

seabreeze

[Indiana shooter]

I had issues with that black or dark brown gritty crud before I discovered this wonderful site. My problem was that I had assumed paraffin wax was a flux that cleaned the lead and re-introduced lost alloy back into the lead. Today I clean my lead long before it makes it to my pot with sawdust and stir my smelting pot with wooden paint mixers. Then after each flux with sawdust I use beeswax to reduce the alloy back in.

[MUSTANG]

Perhaps not a good smelting when originally cast into ingots. Years ago I had similar problems when I just tossed the whole bucket of wheel weights into a large cast iron pot and melted; the rubber parts of the valve stems would turn into a black mess on the top of the melt. Some would inevitably be included in a cast ingot and reappear when melting ingots to cast boolits. Cure is to flux, skim, flux, skim, etc.. until it is all gone.

Anyway; My thoughts on what it might be.

[RogerDat]

black oxides from old lead will rise too. Sawdust or more commonly wood chip pet bedding for rodents, stirred really well with wooden stick followed by any old cheap candle wax. The sawdust and stirring will bring all the impurities to the top for skimming and the wax will drive the good alloy back in.

I do the happy dance if at a garage sale I score a pewter candle stick with a candle in it - that be a twofer.

[popper]

I tried the sawdust, wooden stick, candle wax. Really good for plugging up a bottom pour pot. Now I stir/scrape a LOT, then put a couple layers of paper towel on top and let it get the good stuff back into the mix. Had probably 1/2 # of ?, ran the pot up to 780F, paper on top. Just lifted off the charred paper, skim a little remaining grey crumbly dross, then back down to 725F for casting. Repeat when tossing the sprue back in. When I smelted WW there was a LOT of that black gunk on top and it keeps coming up. Sawdust works fine there, not in the casting pot.

[Smoke4320]

Don't want black scum then
don't get your wheel weights at Kanye's tire shop .. !!!

[bangerjim]

Sounds like poor ingot making back in the day?

I use pine saw dust in my re-melting pots to flux 3X. Never had "crud" in my casting pot because all my ingots are 110% clean and pure. I have not re-melted COWW's in over 2 years. Just not worth the mess and hassle, what with the shortage of Pb ones and the dominance of Zn and Fe weights in every batch. We are saving tons of $$ by casting our own, so don't worry about spending a little money on good clean lead alloys and forget the "free" buckets of dirty old COWW's.

I only use beeswax in my casting pots to REDUCE the wanted metals back in, and skim off the teeny bit of black stuff left by the wax. Clean shiny mirror surface every time! Sawdust in your casting pot will definitely (somehow!) get down in your pour spout and cause problems down the road.

banger

[RogerDat]

The sawdust / wood chips and wooden stick was definitely meant for the smelting pot not the casting pot. I almost never take stuff direct from scrap to casting. Maybe bar or solid wire solder. Otherwise it generally goes through the smelting pot to nice clean ingots first. I ladle cast so no bottom pour to clog and I still do it that way because I don't want "gunk" in my casting pot.

Bucket of dirty nasty WW's makes me Do the happy dance! Banger is just weird don't you know.