What is this $%#&@ frothy junk

Maybe someone with more sense than me can help identify this mystery froth.
Yesterday I got a package of 50 pounds linotype from a high satisfaction rating vendor on ebay. Today I started smelting it down on my homemade smelter. This gizmo is a piece of 5" circular steel pipe with a plate welded on the bottom and I put on old 5" cast iron frying pan on top to hold the heat. Put it atop my Coleman camp stove with the flame at full blast. Have smelted linotype, wheelweights, lead, all with this thing and never had a problem....until today.
This current batch leaves a silver frothy mess on top of the liquid alloy. It won't stir in, and constant application of a propane torch won't melt it. It scrapes off just like beaten eggwhites from a holiday pie. It sets up hard, so it has some alloy in it. The only time I have seen this before was from a batch of wheelweights several years ago when smelting with a Lee pot and I thought maybe some of them were some other metal. I threw that away. I have saved all this mess thinking I could salvage something from it. Have I gotten hold of zinc, or some other junk? Should I save it still and try to smelt it down some other way?
I did not flux the solid letters as I flux alloy when ready to cast.
Shoot out some ideas, I'm at wit's end!

[smilie=b:

It's pretty difficult to tell without knowing the temperature of the melt when all this happened. It does sound, though, as if the frothy stuff has a considerably higher melting point than the rest of the melt.

Lino has the lowest melting point of any lead-tin-antimony alloy, at about 464*F. Other lead-tin-antimony alloys mixed with lino remain slushy but mixed through the potful of metal until their (higher) melting points are reached - they do not form a scum, sludge or froth. It sounds to me as if you have probably got a mixture of metals here, mostly lino but with a bit of something else. If you separate the froth, then melt it and cast it, you can compare its hardness with the lino that has had the froth removed. It could be zinc I guess, but only if your potful of metal is at a pretty high temperature - at least 700*F rather than the 460 required to melt the lino. At temperatures between 460 and 700 it should be forming a pretty solid layer on top of the melt and be fairly easy to remove, so long as you don't stir it in.

If it looks like a gray foam
I had that the last time I did a Lino melt

I raised the temps and stired it in

It diapeared into the pot , still had some of the normal crud on top that I had to skim off

And when I add it to my mix , it works great

John

Lead Melter,

Put it back in the pot, it's what you paid for and what you want!

When I melted monotype/foundry type, I got the same stuff you are referring to. Adding more heat and fluxing will cause it to go back into the solution. I added sawdust and candle wax and lit the mixture. It added quite a bit of heat to the pot and the slush magically disappeared.

John

You mention "solid letters". Was your alloy as individual letters or stips of letters?

If individual letters, you may have monotype rather than linotype. I have found that monotype or foundry type requires a bit more fluxing during smelting to drive the "froth" back into the melt.

Jerry

Your smelting temp is way way too low and you have not fluxed properly. Get a turkey fryer and forget the coleman stove for anything but WW's. (even with them, the turkey fryer is much faster, but you have to keep an eye on it). Monotype or linotype need a good flux and a reasonably high temperature, around 800-850*F. Only wheel weights with the possibility of zinc contamination need a low (<780*) smelting temp. I have good luck with parrafin wax for flux, but everyone has his favorite. If you do it properly when smelting, and make clean ingots, you will not need to flux when casting (or not much and not often). There's no need to stink and smoke up everything when you are casting, and it's not good to gunk up your casting pot. It can cause no end of clogging problems with a bottom pour pot, and you don't need to be breathing the nasty smoke. Put all the "froth" back in and do it right or you will be losing most of the good tin and antimony that are the reason for going with lino or mono in the first place.

I melted 40 pounds of old Linotype still in type form. It was very oxidized and when melted it turned to "foam".
I used a table spoon of plumber's flux and all was well.

Well, I finally took some advice and believe the problem has been solved.
Flux. Flux. Flux.
After I fill the pot with the lino letters, I let it melt, then add a chunk of paraffin about the size of my thumb and ignite it. Then vigorously stir and a lot of the froth melts down. After my last addition of wax, I then add a thimble sized chunk of Frankford Arsenal Clean Cast fluxing compound, let it melt, stir it in, then cover with the frying pan for about 5 minutes. The end result is a hard, crusty slag that spoons off easily. I get about 2 tablespoons of slag from a 12 pound melt. That's a far cry from the 12-15 tablespoons from the original attempt.
Thanks a bunch guys, you saved me a bunch of trial and error, not to mention money in the process.