Keilim, Chapter 12, Mishnah 8. Our Mishnah returns to a fundamental rule about metal keilim: a metal utensil is susceptible to tumah whether or not it forms a receptacle. Unlike keilim of wood, leather, bone and glass, which generally need a hollow that holds something in order to receive tumah, a flat metal implement with no cavity at all is still a kli for these purposes. The Mishnah now brings a list of everyday metal items, none of which holds anything, and rules that every one of them can become tamei.
The list of metal implements
"Ha'olad" is a particular type of metal shears or scissors. "Vehakolmos" is a writing pen, here one fashioned of metal: copper, iron or silver. "Vehametultelet" is a plumb, a weight hung on a cord and let down alongside a wall to check whether the wall is standing straight. "Vehamishkalot" are the metal weights placed on the pan of a scale. "Vehakurin" is a metal tool used in the olive press to pack the olives down into the vat. "Vehakan" is a metal ruler, used for drawing straight lines on a scroll. "Vehakanah" is the metal tablet upon which the parchment was laid while those lines were being scored into it.
Concerning all of them the Mishnah rules "temei'in": every one of these implements is susceptible to tumah. Look at the list and you will notice that not a single one of them contains anything. Scissors, a pen, a plumb, weights, a packing tool, a ruler and a scoring board are all solid, flat or pointed objects with no hollow whatsoever. That is exactly the point. Since they are made of metal, the absence of a receptacle makes no difference at all, and each one receives tumah as a full kli.
Unfinished wooden keilim
The Mishnah continues: "vechol golmei chelei etz temei'in." A golem is an unfinished utensil, one whose body has been formed and which is already usable, but which still awaits its final touches: it has not yet received its rim, or its handle, or some last stage of the craftsman's work. Wooden keilim in that state are susceptible to tumah. The reason is that they can already serve a purpose in their present condition, and a wooden object that can be used is a kli.
Here we meet a genuine difference between materials. With metal we say that the vessel is not susceptible to tumah until the craftsman has completed it entirely. With wood the halachah is otherwise: because the half-finished wooden item is already fit for some measure of use, it counts as a kli and can become tamei.
The exception: eshkero'a wood
To this the Mishnah attaches a limitation, opening with the words "chutz mishel eshkero'a." There is one variety of timber, eshkero'a, whose vessels are left outside the rule. This species is exceptionally hard and stubborn, so that an object shaped from it serves no purpose whatsoever until the craftsman has planed it down and applied the final polish. While it remains in that rough condition nobody is able to put it to any use, and something that cannot be used has not yet entered the category of a kli, so tumah does not take hold of it at all.
Rabbi Yehuda's addition
Rabbi Yehuda widens the exception to a second species with the words "af gerofit shel zayit": a vessel produced from the branch of an olive tree. Such a vessel, he holds, stays tahor "ad shetishalek," until it has been boiled and its sap driven out of it. Olive wood carries a heavy load of moisture and resin, and as long as that liquid sits inside, no one is able to make any use of the vessel. Once it has been set over fire and the sap has been cooked away, it becomes serviceable, and at that point it turns into a kli that tumah can affect.
So our Mishnah gives us two clear principles side by side. Metal needs no receptacle: shears, a pen, a plumb, weights, an olive packer, a ruler and a scoring tablet all receive tumah despite holding nothing. And wood needs no completion, provided it is already usable, with the exceptions of eshkero'a wood and, according to Rabbi Yehuda, olive wood, which remain outside the category of keilim precisely because until the final stage of work they cannot be used at all.