Pot metal, a combination of several types of metal smeltered together, is DEFINITELY a challenge to work on. Different eras of cars used different combinations of metal to make it. Especially nasty on post-war era cars ... I assume it's because most of the "good" metal went into armament and ammo production so automakers were forced to use whatever they had on hand in order to still get the cars off the production line.
My worst experience dealing with pot metal involved a set of gauge bezels from a 1959 Impala. You know, the huuuge 6" wide speedometer bezel with the dual-pod gauge bezels on each side. They were originally chromed but had been sitting in a field for probably 40 years. They were VERY pitted and nasty and needed a lot of help. The two little pod bezels were easy enough to get down to bare metal with some #4 Fine sand in the pot blaster, but that big one had to be sent to my buddy Darrell at ChromeMasters in Nashville. (He charged $20 to dip it / strip it and had it back to me in 3 days; I'd highly recommend him if anyone needs his services.)
I worked on those parts for three weeks. Filling the holes left from the pitting with my magic high temp stuff, sanding, smoothing out the surfaces, sanding some more, gassing them out a half dozen times (to remove those little air bubbles and impurities SweatyBetty referred to), filling and sanding again, and finally powdercoating them in Super Chrome ...... FOUR TIMES! Despite having a very happy customer, they honestly weren't up to my standards at all.
If I ever get more pot metal in that looks like those things did, I'll charge three times as much. I know I lost my a$$ on that job. :love4:
