A tanur that became tamei,

how do we purify it (without completely destroying it)?

One splits it into three (vertically, from top to bottom, so that no one segment was a majority of the oven)

and scraped off the paste (the coating of clay on the outside of the oven walls must also be broken off at the points where it is split, so that this coating does not hold the walls together)

until it is on the ground (i.e. the coating must be removed at the splits from the top all the way to the bottom, in addition the clay that attached the oven to the ground must be removed so that it now rests directly on the ground);

Rabbi Meir says,

it is not necessary

to scrape off the paste,

and not until it is on the ground,

only he must reduce it

from within to four handbreadths (i.e. the interior walls need to be cut merely to the point where less than four handbreadths remain whole);

Rabbi Shimon says,

and it must be moved (i.e. the three sections required by the first opinion must also be separated from each other).

If one split it into two,

one [half] large and one part small,

the large [half] is tamei,

and the small [half] is tahor.

If one split it into three,

one [third] as large as the [other] two,

the large [third] is tamei

and the two small ones are tahor.

פרק ה משנה ח

If one cut it into segments

along its width (i.e. into ring-shaped segments)

shorter than four handbreadths (and less than half the height of the original oven),

it is tahor.

If one covered it in plaster (if one took a tanur that had been disassembled to make it tahor, and then held the pieces back together using plaster or clay layered on their exterior)

it is susceptible to tumah

when it is heated

sufficiently to bake in it a sponge cake.

If the paste was distanced from it (the pieces of the tanur were put back together, but the clay was not plastered directly onto them, but was rather formed into a wall around them separated by a space)

and he placed sand or pebbles between them,

by this they said,

a nidah and a woman who was tahor

can bake in it [together]

and it is tahor (i.e. the oven is tahor).