Pot metal (AKA pig metal) is an alloy of metals with a fairly low melting point. This metal was widely used in the casting of some parts for many radios of the 1920's & 30's such as tuning condensers, frames, dial drums and other parts. Pot metal was also widely used in the automobile industry during that period.

Pot metal has become a negative word for many of us who restore old radios as much of it is known for its tendency to self destruct. We refer to this problem as; "Pot Metal Cancer". However, not all castings were prone to the cancer. If the recipe was followed and not corrupted, pot metal was a good product and fine examples made in the 1920s can be found to this day.

Zinc, lead, aluminum, tin & copper are the ingredients often used in the recipe.  Some of the formulas used would vary and if a known stable formula was not strictly adhered to, deterioration was soon to start.

Another reason for the "cancer" is the formula was corrupted before the piece was cast. This was often caused by the workers who would often shovel up the dross and toss it back in the molten metal. Sometimes they would toss in other materials as well. This unbalanced recipe was the most certain (if not the main) cause for the self destruction of the cast piece.

Because of the instability of some of the metals within the faulty alloy, repairs are not always satisfactory due to the continuing instability. I have repaired pot metal using the steel filled (gray) epoxy (such as JB Weld) with some degree of success. It does a good job but don't be surprised if the piece continues to deteriorate or your repaired piece no longer fits where it should. Pot metal when formulated correctly is very stable and (in my opinion) will likely last indefinitely. I have (in my radio collection) some parts that are over 80 years old that are 100% perfect. However when Pot Metal has become, distorted, swollen, cracked or is in the self destructing process, this will likely continue. There is no way I know of to prevent further deterioration.