Keilim, Chapter 3, Mishnah 4. The previous mishnah dealt with an earthenware vessel that was still whole in one piece but had developed a hole. Our mishnah takes up a parallel question from the opposite direction: a vessel that is technically still one piece, yet so cracked and weakened that it is on the verge of collapsing. Does patching such a vessel restore its capacity to receive tumah, and what happens when a vessel has already broken apart and its shards are pieced back together?
A barrel held together by a coating
The mishnah opens: "Chavit shenitra'a", an earthenware barrel that has become cracked. The cracks have left it so fragile that it can no longer hold even a chatzi kav of figs. In that state the barrel is tahor, because a vessel too weak to serve its purpose is no longer functionally a container for tumah.
Before the barrel actually fell apart, however, its owner treated it: "utafalah begelalim", he smeared its outside with dung. Once the coating dries it binds the cracked walls to one another and reinforces the whole barrel.
Concerning such a barrel the mishnah rules: "af al pi shenotel et hagelalim vehacharasim noflin", even if the deterioration has reached the point that removing the coating would cause the barrel to collapse immediately, so that only the dung is holding the shards in place, it is temei'ah: it counts as a complete vessel and is capable of becoming tamei.
The reason: "mipnei shelo batal shem keli me'aleha", because it never lost its identity as a vessel. True, in its weakened state it had become tahor and could no longer receive tumah. But it never came apart; it remained a single intact barrel, and the name "barrel" never left it. Since the title of vessel was never forfeited, the moment the coating restores its strength and it can once again support a load, it is a complete barrel and receives tumah. Though the walls themselves keep growing weaker, the dried coating is doing the work of holding the vessel together, and that is enough to return its susceptibility to tumah.
This follows the principle of the preceding halachah: so long as the vessel is intact and still bears the name of a vessel, a repair brings it back into the category of a keli for the laws of tumah. Note also that the mishnah deliberately chose dung as the patching material. Dung is not a substance of the same standing as clay, and yet since it succeeds in holding the barrel together, the barrel becomes capable of tumah. The ruling does not depend on which material was used for the patch.
A barrel that actually broke apart
The mishnah now contrasts a barrel that never came apart with one that did. "Nishberah vedibek mimenah charsit", the barrel broke and its own shards were cemented back together, "o shehevi charsit mimakom acher", or he brought shards from elsewhere and assembled them into the form of a barrel, "utafalan begelalim", and then coated them with dung so that the structure would hold firmly.
The ruling: "af al pi shenotel hagelalim vehacharasin omdim, tehorah". Even here, where the shards were joined so securely that they would remain standing on their own if the coating were stripped away, the barrel is tahor.
Here the mishnah's reasoning is precisely inverted: "mipnei shebatal shem keli me'aleha", the title of vessel had already fallen away at the instant of the break. No amount of cementing, and no coating of dung, can restore what was lost then. All that lies before us now is an assembly of fragments arranged in the shape of a barrel, and no arrangement of fragments recreates the keli that once existed. Hence the rule: from the moment of breakage the vessel is tahor for good, and neither gluing nor repair will ever again make it susceptible to tumah.
One case is excluded. If the shards were coated with clay and then returned to the kiln to be fired anew, the status does change, because the firing genuinely produces a vessel: it is a new keli. Our mishnah speaks only of a makeshift arrangement, patching broken shards with clay, dung or adhesive, and such patching has no power to restore the vessel's former standing.
When one shard holds a revi'it
Until now the mishnah dealt with a barrel whose shards were each too small to receive tumah in their own right. The final clause addresses a reassembled barrel one of whose shards was large enough to be a vessel by itself.
"Hayah bah cheres machazik revi'it", one of the pieces cemented into the reconstructed barrel is itself substantial enough to contain a revi'it of liquid. A fragment of that size carries the status of a vessel in its own right, so that already while it lay by itself, before anyone assembled the barrel, it could contract tumah and pass it on to whatever food or drink came in contact with it.
The mishnah rules: "kulah metamei bemaga". Should tumah reach that large fragment, the whole reconstructed barrel, the lesser pieces cemented to it included, transmits tumah to food and drink by touch. "Ukenegdo metamei ba'avir", yet tumah through the airspace of a vessel operates only within the hollow of that one fragment, the area bounded by its own walls, and nowhere else in the barrel.
The reasoning is clear. That sizable fragment retained its standing as a keli throughout; it was liable to tumah and transmitted tumah through its airspace before anything was cemented to it, and attaching the remaining pieces changes nothing in that regard. The lesser fragments, as we have learned, do not qualify as earthenware vessels at all, so airspace tumah is beyond them. Their role is that of a yad, a handle serving the large fragment to which they were fixed. And since handles of an earthenware vessel pass tumah on only by contact and never through airspace, the same holds for these cemented pieces: attached to a tamei fragment that never forfeited its status, they convey tumah by maga, by touch and nothing more.