Kelim, Chapter Seven, Mishnah One
1) The fire-basket of a householder which was lessened by less than three handbreadths is susceptible to impurity because when it is heated from below a pot above would still boil.
a) If [it was lessened] to a lower depth it is not susceptible to impurity.
2) If subsequently a stone or gravel was put into it, it is still not susceptible to impurity.
3) If it was plastered over with clay, it may contract impurity from that point and onwards.
4) This was Rabbi Judah’s reply in connection with the oven that was placed over the mouth of a cistern or over that of a cellar.
Section one: The fire-basket referred to in our mishnah is a portable earthenware stove. The bottom was thick so that it could be placed on any surface. Coals would be placed inside and the pot would be placed on top. If the fire-basket was reduced, meaning the bottom was further from the top, but the reduction is less than three hand-breadths, it is still susceptible to impurity because it is still usable. However, if it was lessened more than three handbreadths, it is pure because the fire-basket is not usable.
Section two: Putting stone or pebbles into the stove to fill in the gap does not restore the fire-basket to its original state and therefore it remains impure.
Section three: However, if he put in stones or pebbles and then plastered them over with clay, they again become susceptible to impurity.
Section four: This section refers to mishnah 5:6, where Rabbi Judah and the sages had a dispute concerning an oven placed over the mouth of a cistern or a cellar. According to Rabbi Judah the oven was not susceptible to impurity unless the fire in the pit could heat it sufficiently. According to our mishnah, he referred to the fire-basket to prove his point. The fire-basket is not impure unless the coals in the bottom are close enough to the top to heat up the pot.