Kelim, Chapter Fourteen, Mishnah Six
1) A metal basket-cover which was turned into a mirror:
a) Rabbi Judah rules that it is clean.
b) And the sages rule that it is susceptible to impurity.
2) A broken mirror, if it does not reflect the greater part of the face, is clean.
Section one: Had it not been made into a mirror, all would agree that this metal basket-cover is pure because it is a metal object used for the purposes of a wooden object (see 12:6). As we learned, in such cases the vessel has the status of being made of wood. However, if he polishes it and makes it into its own vessel to be used as a mirror, it is susceptible, according to the sages. Rabbi Judah holds that it is still not considered a vessel and it is still pure.
Section two: If the broken mirror cannot show most of a person’s face, it is no longer susceptible to impurity because it is really not usable. But if it can still reflect most of the face, it is still usable.