Kelim, Chapter Eleven, Mishnah One
Chapters eleven through fourteen deal with purity issues related to metal vessels.
1) Metal vessels, whether they are flat or form a receptacle, are susceptible to impurity.
2) On being broken they become clean.
3) If they were re-made into vessels they revert to their former impurity.
4) Rabban Shimon ben Gamaliel says: this does not apply to every form of impurity but only to that contracted from a corpse.
Section one: Metal vessels are susceptible to impurity whether or not they have a receptacle. This distinguishes them from other material (woodsee 2:1) which needs to have a receptacle.
Section two: If they break such that they are no longer usable, they become pure again.
Section three: If they are re-fashioned, their original impurity is restored to them. In other words, they don’t only become susceptible to impurity, they actually get their old impurity back. In the Talmud, it is explained that this was a rabbinic decree made by Shimon ben Shetach, a Second Temple sage. According to the rules of the Torah, once the metal vessel has been broken, it does not go back to its former impurity.
Section four: Rabban Shimon ben Gamaliel limits this rabbinic decree to a case where it had contracted corpse impurity. If it had been defiled in some other, less significant way, then it does not revert to its former impurity.