Much of the week we have been discussing the tanur -- earthenware oven. Recall that the tanur in the times of the Mishnah was a cone-like shaped earthenware vessel that was open at the top and bottom -- it had not base. It was generally cemented to the ground, with the dough being stuck to the walls when baking.
The Mishnah (5:9) discusses a case of an oven that came from the factory in vertical slices. The Mishnah teaches that once the oven is constructed and rings placed around it to hold the slices in place, the oven is then susceptible to tumah. The Mishnah continues that if the oven becomes tameh and the rings were then removed, the oven is considered broken (Bartenura), and the parts are tahor. The oven would only then become susceptible to tumah if the oven was put back together again, rings added and coated with clay. It would immediately be so, even if the oven had not yet been fired up. This is in contrast to a newly manufactured oven, that only becomes susceptible to tumah if enough heat has been generated inside it to back soft cakes.
The Mishnah Achrona cites the debate regarding the first time this oven is put together. Note that the Mishnah says that the oven is susceptible to tumah once the rings are placed around the oven; there is no additional requirement of coating it with clay. Why does this requirement appear the second time the oven is pieced together but not the first? What is the basis for the difference?
The Rambam explains that after the rings are removed, the oven is considered broken. As we learnt previously, once a kli cheres is broken it is no longer susceptible to tumah and that does not change by simply putting the pieces together again. It only becomes susceptible to tumah if the parts are used to make a new vessel -- which is satisfied with the addition of the clay. In our case, when the parts initial arrive, they are not considered a broken, since they were never a kli. It is with the addition of the rings that the oven first become defined as a kli.
The Rash and Rosh however argue that there is no difference between the first and second construction, and in both situations the oven becomes susceptible to tumah only with the additional clay coating.
Considering that when the rings are removed the tanur is considered broken, one might ask why the oven is immediately susceptible to tumah when the rings are returned and the oven recoated. In the previous Mishnah we learnt that if an oven was sliced horizontally into loops (less than four tephachim thick) then the oven is tahor. If it was then put together again and coated with clay, it only becomes susceptible to tumah after it has been fired up to the degree required by a new oven. Why is this case different?
The Tifferet Yisrael suggest that our case is different since the rings provide strong structural support. This is unlike the previous Mishnah where the parts of the oven are held together with newly applied clay. In other words there are structural differences. The novelty in the opinion of the Tifferet Yisrael is that firing of the oven is only required for susceptibility to tumah when it serves to provide the necessary strength to the kli. In our case, that is satisfied with the loops.
The Mishnah Achrona however explains that in our case since the parts had initially been fired before delivery, it is not necessary to fire them again. The case in the previous Mishnah however is worse. Since the oven was sliced, the initial firing is disregarded and the process is again required. We find that according to the Mishnah Achrona, the firing of the oven is necessary to define the oven as a kli. The difference between the two cases is simply whether that process has been satisfied.
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