Keilim, Chapter 11, Mishnah 3. This chapter deals with the tumah of metal kelim, and our mishnah continues a discussion that opened just before it. The rule we were taught is this: when a metal keli that is tamei breaks, and afterwards the metal is refashioned into a new keli, the new keli resumes the very tumah that the original keli carried before it broke. This is a decree of the chachamim rather than a Torah law, and it applies not only where we know for certain that the earlier keli was tamei, but even where it merely might have been. That is why a person who comes across a metal keli and has no idea where its metal came from, whether from a tamei keli or from metal that was never tamei at all, must treat that keli as a safek tamei.
Our mishnah now turns the picture around and lists the exceptions: cases where we need not worry at all, because we can identify the source of the metal and we know that the source could never have carried tumah.
Metal whose origin is clean
"Ha'oseh kelim min ha'eshet": one who fashions kelim from iron taken straight from the place where iron is extracted. Here the metal is fresh, drawn directly from its source, and it never passed through any keli. "Umin hahararah": or from a fresh mass of metal, metal that took its shape at the moment it was formed and was never anything else. Such metal could not have been tamei.
"Umin hasoveiv shel galgal": from the iron hoop that runs around a wagon wheel. That band is fitted over the wooden wheel to protect it from the rocks it rolls over, so that the wood will not split apart. An object of this sort never enters the category of things susceptible to tumah at all, since tumah takes hold only where a keli is used by a person himself, and not where the item was built merely to safeguard a different vessel. Even when its history is entirely unknown to us, then, there is nothing here to suspect.
"Umin hatasin": from sheet metal. "Umin hasipuyin": from metal plating, the kind of thin plating that was laid over another material as a surface. Neither of these is a keli in its own right, so neither of them could ever have become tamei.
"Mikannei kelim": from the metal stands of kelim, the ring or footing upon which a vessel is set down. Tumah has no hold on a piece like this, because its function lies wholly in the service of the vessel and not in the service of a person. "Mozenei kelim": from the metal handles by which kelim are carried. These too stand outside tumah for precisely the same reason: they exist for the sake of the vessel they are attached to.
"Umin hashecholet": from the scraps of metal that come away from a keli while it is being manufactured. "Umin hagerudot": from the filings that are shaved off a keli in the course of its production. In both of these cases the metal was separated from the keli before the keli was ever finished, and an incomplete keli is not susceptible to tumah, so these bits could never have been tamei.
The mishnah's verdict on all of the above: "tehorin." Kelim produced from any of these materials are pure. In none of these instances is there room to suspect that the metal was once part of a tamei keli, so when such a keli stands before us we know its origin was clean.
Rabbi Yochanan ben Nuri and pieces cut away
Rabbi Yochanan ben Nuri adds one further item to the list of exceptions: "af min haketsutsot," also from cut-off pieces. A person who gathers chunks that were severed from a metal vessel and works them into a new keli has produced something that is tahor.
To appreciate his point, we need the reasoning behind the original decree. Why did the chachamim rule that a keli refashioned from a broken tamei keli carries its old tumah? Because of a concern about shortcuts. Imagine a person whose metal utensil became tamei and who wanted a simple way to purify it. He could puncture it, patch the hole, and announce that it is now a brand new keli and no longer impure. But if the hole he made was not large enough to render the keli broken in halachah, the keli remained tamei all along, and he would go on using a tamei utensil without knowing it. To close off that danger, the chachamim declared that even after it is repaired the keli remains tamei.
Rabbi Yochanan ben Nuri argues that this concern has no place where the pieces were cut away. There is no chashash that the person did not do a thorough job, because he is not making a small puncture at all: he is breaking the keli apart entirely. With the worry removed, the decree has nothing to stand on, and so cut pieces of metal taken from a keli are considered tahor as well.
Where the concern does remain
The mishnah returns now to materials whose past does give us reason to worry. "Mishivrei kelim": a fresh metal keli fashioned out of shards of metal kelim. "Min hagerutin": out of small fragments that fell away from metal kelim once those kelim had worn down through use. "O min hamasmerot sheyadua shena'asu mikelim": or out of nails that we know for a fact were produced out of metal kelim. In all three instances the ruling is "temei'in": the newly made utensils are impure, since the vessels that supplied their metal may well have been carrying tumah. Their earlier status is simply beyond our reach, and it is exactly against such a possibility that the chachamim directed their decree.
Nails of unknown origin
The nails treated until this point were ones whose manufacture out of kelim is established. The closing clause of the mishnah takes up a different case: nails about which nothing at all can be established. Perhaps someone shaped them out of old metal vessels, and perhaps they were hammered out of iron that came straight from the ground.
"Min hamasmerot": concerning new kelim made from such nails, "Beit Shammai metam'in", Beit Shammai rule that the new kelim are tamei, "u'Veit Hillel metaharin", while Beit Hillel rule that they are tahor.
Beit Hillel base their leniency on a safek sefeika, two successive doubts, each of which leans toward purity. Doubt one: the nails may well have been drawn from newly mined iron, and metal of that kind is tahor beyond question. Doubt two: even granting that older vessels were their source, those vessels themselves may never have contracted tumah at all. Once the doubts pile up in this way, Beit Hillel declare the finished keli pure.
Beit Shammai rule that such utensils are tamei. They fear a slide in practice: if this case is permitted, people will end up applying the same leniency to a keli built from nails whose origin in older vessels is not in doubt whatsoever. Rather than draw fine distinctions, Beit Shammai prefer chada gezeirah, a single sweeping decree that takes in every utensil of this sort, leaving no opening for laxity. Beit Hillel, for their part, hold that the rabbinic safeguard was never legislated with a case like this in view.
So this mishnah gives us both sides of the decree's boundary line: the materials whose purity we can trace with confidence and which therefore yield a keli that is tahor, and the materials whose past we cannot recover, where the chachamim's safeguard remains in force.