Keilim, Chapter 15, Mishnah 3. This mishnah turns our attention to the flour sifter, a utensil built from two distinct parts: a wooden frame and a mesh screen stretched across it. At first glance a sifter hardly seems like a receptacle at all, since its whole purpose is to let the flour pass through. Nevertheless, the screen does hold something: it traps the coarse bran and the unwanted matter that must be separated out of the mixture. Because it retains what it is meant to retain, the Mishnah treats it as a genuine container, and it is capable of receiving tumah even on the Torah level.
The question the mishnah addresses is narrower and sharper: what is the status of the screen by itself, once it has been lifted out of its wooden frame? Is it still a kli, or is it now merely a detached piece of a utensil, no different from a fragment of something broken?
The professional sifter
The Mishnah begins: "Nafah shel salatin tamei" - the hair screen belonging to the sifter of those who sift flour professionally is susceptible to tumah, and this remains true even when the screen has been taken out of its frame. Removal does not reduce it to the status of a broken vessel, because for the professional this is simply part of how the utensil is used. Someone who sifts flour in large quantities lifts the screen out regularly in order to clear away the bran and the debris that lodge in the holes, and then sets it back in place. The sifter is built to come apart and be reassembled. A screen out of its frame is therefore not a ruined object but a working component of a functioning utensil, resting between one use and the next, and it retains its capacity to become tamei.
The household sifter
The Mishnah continues: "Veshel baalei batim tahor" - but the screen of a sifter used by ordinary householders in their homes is tahor once it has been detached. In a private home the sifter is not in constant service, and there is no regular routine of dismantling and cleaning it. Its screen was never meant to lead an independent existence. Once it has come out of its frame, it is regarded as a broken utensil, no longer a working kli, and it is not subject to tumah at all. The identical piece of mesh has two different halachic lives depending on whose hands it serves: for the professional it is a part awaiting reassembly, and for the householder it is simply a piece that has come off.
Rabbi Yehuda and the hairdresser's screen
A final ruling is appended in the name of Rabbi Yehuda, concerning the hair screen used by a woman whose trade is plaiting and setting hair. Of hers too, he says, "af shel godelet", the screen is "tamei moshav": it can contract the tumah of a seat, known also as tumat midras. That category of tumah attaches to objects whose function is to bear a person's weight, whether one sits on them or leans upon them; when someone in a state of tumah presses his weight down on such an object, the object itself becomes tamei.
Why should a mesh screen fall into that category? The Mishnah explains: "mipnei shehabanot yoshvot betocho vegodlot" - because the girls would sit on it while their hair was being braided and arranged. The screen served a double purpose in the hairdresser's hands: it caught the loose hair and whatever else fell during the work, and at the same time it functioned as the seat on which the girl sat. Since it is genuinely designated as a place to sit, Rabbi Yehuda rules that if a person who is tamei sits upon it, this screen contracts tumat midras.
Our mishnah has thus taught us that a utensil's status is measured by the life it actually leads. The same hair screen may be a living part of a working sifter, a discarded fragment, or even a seat, and its susceptibility to tumah follows the role its owner has given it.