Gray stuff on top of melt

[ChuckS1]

Okay, now that I've been casting for a few weeks and have made some pretty good bullets (IMHO, anyways), I've got a pretty dumb question...

I have a Lee 10# pot (that doesn't drip anymore) and I usually fill it up with WW and 6 ounces of 50/50 bar solder. I flux with a sugar cube sized piece of paraffin. After it burns off, there's the gray powdery stuff I skim off and toss. Comes out as a nice powder, but hardens as it cools.

What is that?

[runfiverun]

i would call it slag
but it could be antimonial oxides.

[Buckshot]

............You stir the melt as you're fluxing, right? Pushing the crap and crud under the surface and working it to one side as the flux is still present. If not then add bit more. You should be spooning out pretty much only a black powdery-grainy residue and the surface of your alloy should be as clear and shiny as Mercury. An oxide layer will begin to form shortly thereafter, but for now it's fluxed.

...............Buckshot