An oven that was heated from the outside, or that was heated without his intent, or that was heated in the artisan’s workshop, is tamei. It once happened that a fire broke out among the ovens of Kefar Signah, and the case came to Yavneh, and Rabban Gamliel ruled [the ovens] tamei.

The supplement of the oven of householders is tahor, but that of bakers is tamei, because he supports the spit on it. R’ Yochanan HaSandlar says: Because he bakes with it when he is hard pressed. Similarly, the supplement of the cauldron of olive boilers is tamei, but that of dyers is tahor.

An oven that was filled with earth up to its midpoint: [The area] from the earth and downward contracts tumah via contact; [the area] from the earth and upward contracts tumah via airspace. [If] one placed [an oven] over the mouth of a pit or over the mouth of a cistern and placed a stone there, R’ Yehudah says: If he lights [a fire] below and [the oven] is heated above, it is tamei. But the Sages say: Since in any event [the oven] was heated, it is tamei.

An oven that contracted tumah, how is it rendered tahor? One divides it into three [sections] and scrapes off the [clay] coating down to the ground. R’ Meir says: It is not necessary to scrape off the [clay] coating nor [is it necessary to divide it] down to the ground; rather, one reduces it from within [to less than] four handbreadths. R’ Shimon says: And it must be moved. [If] one divided it into two [sections], one large and one small, the larger [section] is tamei and the smaller [section] is tahor. [If] one divided it into three [sections], [such that] one [section] was as large as [the other] two, the larger one is tamei and the two smaller ones are tahor.