Count me among the ones who played. My grandfather worked for AC Gilbert, who's company originally produced The Erector Set. It produced many toys, and we had one of these lead casting kits: http://www.girdersandgears.com/kaster.html
I never could figure out one of the molds, which is fortunate because it produced a whistle. In lead. That you stick in your mouth. Maybe I couldn't figure out how to assemble it because I was already too stupid from the lead poisoning due to the fumes while pouring the other molds.
But I have to say: Working with a crucible of molten lead was pretty fun as a kid.