Hey guys, I have been casting for only about 10 years, and still wonder what I am skimming off my pot. I flux with Marvellux, and on my clean lead I get a grayish stuff that comes to the top. I generally don't get much, and always thought it might be zinc, but my brother who lets his heat up more before fluxing gets alot more of it than me, and it's heavy. Are we cooking something important like antimony out of our mix, or is it something unimportant?. I am otherwise happy with my bullets, and they outshoot anything I have ever bought. Thanks for the help.