[If] one cut [the oven into] segments along its width, [each segment that is] less than four handbreadths is tahor. [If] one plastered it with clay, it becomes susceptible to tumah from when he heats it enough to bake sponge cakes in it. [If] one distanced the [clay] coating from it and placed sand or pebbles between them, of such [an oven] they said: A niddah and a woman who is tahor may bake in it and it is tahor.