I'm not sure what all it is used for but I do know that they frequently used them for wheel weights and when they get mixed in with the lead wheel weights, it all turns to sludge resembling your photo.   I can't imagine any reason for it to have caused your pot to fail?

Zinc? Would be my bet.

Good idea Kees. I live about 150 yds. away from a Family Dollar store. But it's not that thrifty.

Yep I really like Libby, fun shoot twice a year.
 Eureka Montana has the David Thompson days shoot end of the month but I'll miss that one.
Kevin

Never did make it to the Libby RDV.  Oh well...
I got to the Eureka event several times.  The first one I won the shooting event.  A few years later I returned and somehow won the best beard contest.  I bought a Douglas 1 x .54 barrel and had it installed on my Renegade.  That was really a shooter after that.  Like a damn fool, I sold that rifle.      There used to be a bunch of Canadian guys that would come down for the fun and merriment.  I really liked them.  At the time I had a bunch of BP revolvers and I would outfit myself like Josie Wales, probably had half a dozen pistols in holsters and stuffed into my belt.  We used to have shootouts and I was pretty formidable with all those guns.  One of the Canadians had a "hanging" harness and he always got lynched.  He had the kick and quiver routine down pretty good.
Go to Eureka, Kevin.  Go!!!

John (Bigsmoke)

Good advice. I don't do the lottery thing anyway. But my wife does. I think I found the problem. I decided to heat the pot again to help remove what's in the bottom of the pot. I think my pot bought the big one. It is not heating up. Has anybody else had their pot quit working in the middle of a melt? I think it makes sense. I bet this stuff would melt if my pot was heating.