Commentaire sur Kéilim 8:9

בור שיש בו בית שפיתה (a smelting pot which has a bottom or foot on which it can rest – a hole in the ground with an arrangement for putting a pot over fire) – a person who digs in the ground and plasters over the spot over with clay/mud and the plaster can stand (or form a vessel) on its own, such as the oven the son of Dinai, as is taught in the Mishnah above in the chapter “A Baking Oven, its Beginning/"תנור תחלתו" (see Tractate Kelim, Chapter 5, Mishnah 10 at the conclusion- who, according to Bartenura, states that he was a robber and would bake his bread in an oven like this and make these kinds of ovens, or a place where trials took place frequently; see also Tractate Sotah, Chapter 9, Mishnah 9, where this name also appears). But there are those who have the reading of כור/smelting pot with the letter כ'/Kaf (and not the ב'./Bet – as found in our editions of the Mishnah) – and it is a utensil/vessel in which they smelt in it gold and the silver and metals, he language of an iron furnace/כור ברזל. But to me, it appears that it is an oven of a blacksmith.

A pit which has a place on which a pot may be set is unclean. The pit to which this section refers is an oven placed into the ground and attached to the ground with clay. There was a place on top where they could rest a large pot. Since it is an oven, and it can be used to make food, it can contract impurity.

פורנה (a stationary large baking oven) – a large earthenware oven and its opening is at its side like our eye. But it is pure, because it is used with the ground, as is taught in the Tosefta (Tractate Kelim Bava Kamma, Chapter 6, Halakha 17).

And so also an oven of glass-blowers, if it has a place on which a pot may be set, it is unclean. Since this oven can be used for cooking food, it too is susceptible to impurity, as long as it has a place on it upon which one could balance a pot.

לזבז – a thick rim.

The furnace of lime-burners, or of glaziers, or of potters is clean. The furnace used by lime-burners, glaziers or potters is not made for cooking or baking and therefore it is not susceptible to impurity, even if it has a place on which a pot can be placed. In other words, whereas the oven used by glass-blowers is also made to be used for cooking or baking the oven used by these three professions is not.

אסטגיות (rims, moldings around a stove) – perforations similar to those that they make for ovens.

A purna: If it has a frame is unclean. Rabbi Judah says: if it has coverings [for compartments.] Rabban Gamaliel says: if it has edges. A purna is an oven similar to the ovens that we use today. It has a hole in its side, and one doesn't stick the bread to the side as was typically done with ovens during the mishnaic period. Rather the bread was put into bottom of the purna-oven as we do today. There are three different opinions as to what the purna needs for it to be susceptible to impurity. The first opinion holds that if it has a frame around it upon which one could balance a pot, it is susceptible. If it has no frame, and only the ground part of the oven is used for cooking, then it is not considered to really be an "oven" and it is not susceptible. The second opinion holds that if it has covered compartments it is susceptible. The third opinion is that it needs edges upon which one could balance a pot. Without at least one of these three things, the purna is simply some clay attached to the ground to keep the heat in, and none of it is used for actual cooking. Such a simple oven is not susceptible to impurity.

שפיות – a thin rim. But the Halakha is according to the first Tanna/teacher. But my Rabbis explained that a לזבז/thick rim and אסאגיות/rims, moldings around a stove and שפיות/thin rims are all one [thing]. But they do not disagree other than that each one was different according to the language that he heard from his master, and a person is obligated to state [something] according to the language of his teacher (see also Tractate Eduyot, Chapter 1, Mishnah 3).