Keilim, Chapter 5, Mishnah 2. This chapter deals with earthenware baking and cooking installations and the point at which they become vessels capable of contracting tumah. Our mishnah turns from the tannur, the oven, to two smaller appliances: the kirah and the kupach.
A kirah is a stove whose upper surface has room for a pair of pots; the kupach is its smaller relative, with room for only one. Each was formed as a hollow earthenware body, closed on top except for the openings cut into that surface, into which the pots were lowered so that the flame underneath would cook what they held. Their walls ran straight up, in contrast to the tannur, which was broad at its base and narrowed as it rose. And whereas a tannur was built for baking, these two served for cooking, which calls for less heat than baking does.
The Minimum Height of a Kirah
The mishnah opens: "Kirah, techilatah shalosh, usheyareha shalosh", a kirah, at its outset three, and its remains three. A newly fashioned kirah must measure no less than three etzba'ot (fingerbreadths) in height; anything lower does not qualify as a kirah. And should it later fall apart, the surviving portion must still reach three etzba'ot if it is to keep the name kirah and remain capable of receiving tumah.
Why does three etzba'ot suffice here, when a tannur is given a measure of four tefachim? Because in a tannur both the wood and the dough go inside, so the cavity has to be roomy. In a kirah the pots sit above the appliance rather than within it. The hollow beneath holds nothing but what burns, and for that purpose a height of three etzba'ot is entirely adequate.
When Is the Kirah Considered Finished?
Height by itself does not yet expose the kirah to tumah. Vessel status arrives "misheyitgamer melachtah", when its production has been carried through to the end. And what marks that endpoint? The mishnah asks, "Eizehu gemar melachtah?", and answers: "misheyasikennah kedei levashel aleha", when it has been heated enough to cook upon it "beitzah kalah shebabeitzim, terufah untunah be'ilpas", the fastest-cooking egg there is, meaning a hen's egg, whisked and poured into an ilpas (a stew pot) that has already been warmed.
Notice how small a quantity of heat this describes. The egg has already been taken from its shell and beaten, and the ilpas into which it is poured has already been heated. Such an egg needs only the slightest warmth to cook. That minimal firing is the measure by which the craftsman's work on a kirah is deemed complete, and from that moment the kirah can contract tumah.
The Kupach: It Depends What It Was Made For
The mishnah now turns to the kupach. It closely resembles the kirah, but with a single opening on top for a single pot. Being narrower, its heat is more concentrated and contained, and consequently it burns hotter. For that reason people would sometimes use a kupach not only for cooking but for baking as well.
Its classification therefore tracks what the owner intended. "Hakupach", says the mishnah, "asaho la'afiyah", if he produced it for baking, then "shiuro katannur", it is gauged the way a tannur is gauged: firing sufficient to bake those light cakes, the sufganin named in the previous mishnah. "Asaho livishul, shiuro kakirah", if he produced it for cooking, the kirah's standard applies: heat enough to cook a whisked hen's egg in an ilpas that is already hot. Short of that, it is not yet a completed vessel, and tumah has no hold on it.
The Stone Handle
From the appliances themselves the mishnah moves on to stones jutting out of them. "Ha'even hayotzei min hatannur", a stone protruding from a tannur's side to the length of a "tefach", or protruding from a kirah's side "shalosh etzba'ot", three fingerbreadths, is "chibur", attached, that is, halachically part of the appliance. Should the tannur or the kirah become tamei, that stone takes on the tumah along with it.
This deserves a moment's attention. A stone utensil ordinarily does not contract tumah at all. But when a stone is affixed to a vessel of another material and serves as its yad, its handle, the Torah teaches that it takes on the tumah of the vessel it serves.
These figures, though, function as ceilings. Whatever length of stone reaches beyond a tefach on a tannur, or beyond three etzba'ot on a kirah, is no longer reckoned as attached, and that surplus remains tahor. Only the stretch lying close to the appliance is treated as belonging to it.
Here too the kupach is judged by the job assigned to it: "Hayotzei min hakupach", regarding a stone protruding from a kupach, "asaho la'afiyah, shiuro katannur", if he built the appliance for baking, the tannur's figure governs, so a full tefach of the stone is drawn into the tumah; "asaho livishul, shiuro kakirah", if he built it for cooking, the kirah's figure governs, and no more than three etzba'ot of stone become tamei with it.
Rabbi Yehudah's Qualification
The mishnah now narrows these limits to specific conditions. "Amar Rabbi Yehudah": Rabbi Yehudah testifies that when the Chachamim declared anything past a tefach detached from the tannur, "lo amru tefach", they stated that tefach "ela bein hatannur lakotel", only with reference to a stone lying in the gap between the tannur and the wall of the room.
The logic is practical. In that position, the surplus length of the stone is precisely what keeps the tannur from being set flush against the wall. The owner is bound to trim it away sooner or later, so the excess is not treated as a genuine part of the tannur. But where the stone is not wedged between the tannur and the wall, there is no reason to expect it to be cut back, and the whole of it counts as part of the tannur and becomes tamei together with it.
Two Ovens Sharing One Stone
The mishnah closes with a further case: "Hayu shenei tannurim semuchin zeh lazeh" - if two ovens stood near one another and were joined by a single long stone, "noten lazeh tefach velazeh tefach, vehashe'ar tahor" - we allot a tefach of the stone to the one and a tefach to the other, each measured from the oven beside it, and the remaining middle portion stays tahor and does not contract tumah with either of them.