Keilim, Chapter 17, Mishnah 17. This mishnah presents a series of wooden and woven articles used by craftsmen and shopkeepers, and asks about each one the same basic question: is this item a genuine receptacle, a beit kibul, or is it essentially a flat surface? A wooden vessel receives tum'ah only when it holds something; a flat wooden utensil with no cavity does not. The mishnah then turns to items woven from straw and reeds and asks whether they are sturdy enough to be called a kli at all.
The craftsman's under-tray
"Tachtit hatzorfim teme'ah": the wooden tray that lies beneath the workplace of a goldsmith or silversmith is susceptible to tum'ah. These craftsmen would sit at their work with a rimmed wooden tray positioned underneath them, and as they filed and shaped the metal, the tiny shavings of gold and silver would fall in and be collected there. Since the rim makes the tray into something that genuinely holds its contents, and those contents are precious, it counts as a receptacle and can become tamei.
The smiths who work in iron, the napachim, sit at a tray of exactly the same design, yet the mishnah rules of theirs: tehorah, it cannot become tamei. The rim may be identical, but the flakes of iron that fall from such work have no value whatever, and nobody troubles to gather them. Consequently the tray was never fashioned with the aim of holding its contents, and an object built without any intention of containing is not counted a beit kibul at all, so tum'ah has nothing to take hold of.
The sharpening board
The mishnah's next item is the mashchezet, a wooden block on which knives were sharpened. If it is one sheyesh ba, which contains, a beit kibul shemen, a small scooped out place for oil, the ruling is teme'ah. Oil was applied to the surface of the block during the sharpening, and the little scooped out space where that oil sat is a genuine cavity. On account of it the entire block is reckoned an object that holds something, and it accordingly comes within tum'ah.
"Veshe'ein ba, tehorah": a sharpening board with no hollow for oil is tahor. Without any cavity it is nothing more than a flat wooden implement, and flat wooden utensils do not become tamei.
The writing tablet
Third comes the pinkas, the wooden tablet on which people wrote. When it has a beit kibul sha'avah, a place that holds the wax, the ruling is tamei. A storekeeper kept such a tablet spread with wax and incised his notes into it with a stylus. Tablets of this sort were manufactured in more than one way: certain ones were plain boards, others carried wax laid over the face of the board, and still others were built with a ridge running round the edge so that the wax was held in place. It is this last type that the mishnah has in mind, and precisely because the raised edge makes the board into something that keeps its wax inside, it ranks as a receptacle and is open to tum'ah.
"Veshe'ein bo, tahor": a tablet with no rim to hold the wax is tahor. There the wax is merely smeared onto the surface, and the board itself contains nothing, so it remains a flat wooden utensil that is not susceptible.
Articles woven from straw and reeds
The mishnah now moves to vessels fashioned from straw, reeds and similar growths. Such an article is treated like a wooden vessel: if it is sturdy and made to last rather than something thrown together temporarily, and it has a receptacle, it is susceptible to tum'ah. A mat woven from straw or reeds that is made for lying or sitting upon takes on the status of bedding, and can therefore contract tum'at midras.
Two items are now brought as a case of dispute: machatzelet hakash, a mat plaited out of straw and intended to be sat upon, together with shefoferet hakash, a straw tube fashioned to serve as a holder. Concerning both, the ruling of Rabbi Akiva is metamei, they do come within tum'ah, for to his mind straw has enough substance for what is made from it to qualify as a kli. The opposing view is that of Rabbi Yochanan ben Nuri, whose ruling is metaher: neither item is susceptible, since straw is simply not lasting enough for such articles to earn the name of vessels.
To this Rabbi Shimon appends a further case, af shel paku'ot, and likewise those made of gourd or pumpkin stalks, kayotzei bahen, they belong to the very same class as the straw ones. In other words, when a mat or a tube is produced from such stalks, the identical argument governs it: one of the two Tannaim would declare it susceptible to tum'ah, and the other would declare it tahor.
"Machatzelet kanim veshel chilef, tehorah": a mat woven of reeds, or of that particular coarse grass, is tahor. Such a mat is too stiff and rough to sit on comfortably, so it is normally not produced for sitting; it is made to provide shade. Since it is not designated for sitting or lying, it has no way of becoming tamei.
The closing case is the shefoferet hakaneh, a length of reed, shechatachah lekabbalah, which someone trimmed and opened up so that it could serve as a holder. Its status is tehorah, and it stays so, says the mishnah, until sheyotzi et kol hakash shebah, until he removes every bit of the white pith that fills the reed inside. So long as that soft interior has not been taken out, nothing can actually be placed in the reed and it is no receptacle; only when it has been fully cleared out does it become a kli into which tum'ah can enter.
Across all of these cases the mishnah works with one consistent measure. Wood, straw and reed become vessels that receive tum'ah when they truly hold something: a rim that gathers precious shavings, a hollow that stores oil, a border that keeps the wax in place, a tube emptied of its pith. Where the item is merely a flat surface, where its contents are worthless, or where the material is too flimsy or the shape too rough for the intended use, it stays tahor.