Negaim, Chapter 11, Mishnah 5. This chapter deals with nigei begadim, the tzaraas of materials, which the Torah restricts to garments of tzemer rochel (lamb's wool) and of pishtan (flax), and to oros, animal hides. Our mishnah takes up two subjects: first, how we judge a woven garment when its threads are not all of one color, and then which shades of nega actually render such a garment tamei.
A garment of two colors: shesi and erev
Weaving involves two sets of threads. Picture a standing loom: one set of threads runs up and down, and a second set is passed back and forth across them. Some mefarshim dispute the identification, but most hold that the shesi is the set running vertically and the erev the set running across. This discussion applies to woven materials of flax or wool, of course, since hides are not woven.
Recall the rule established just before this: a colored garment is not susceptible to nigei begadim, while a white one is. What happens, then, when one set of threads is colored and the other is white? The mishnah says: "begged shesheshiyo tzavua ve'eirvo lavan", a garment whose shesi is colored and whose erev is white, and the reverse, "eirvo tzavua vesheshiyo lavan", its erev colored and its shesi white. In each case one component would be excluded from tumah and the other included. The mishnah's ruling: "hakol holech achar hanireh", everything follows what is visible on the surface.
The Tiferes Yisroel treats this at length. The determining factor is what the eye sees, and this can outweigh mamashus, the actual substance and thickness of the fibers underneath. In the weaving process fine hairs of wool work their way up, and what lies beneath may be of one color while what shows on top is of another. It is the visible surface that decides.
The Rav sets out the practical rule. "Bistam begadim", in ordinary woven garments, it is the erev that is seen, because the cross threads pass over the vertical ones and cover them completely. "Bekoryam uksosos", in the coverings of mattresses and pillows, it is the shesi that is seen. And he concludes that it all depends on the type of craft being practiced. The Tiferes Yisroel explains that in mattress and pillow coverings the threads are drawn extremely tight, and the result is that only the shesi remains visible. In every case, then, we look to the nature of the weave and judge accordingly.
The colors that bring tumah
The mishnah continues: "habegadim mitamim biyerakrak shebiyerokim uvi'adamdam shebi'adumim", garments become tamei with the greenest of the greens and the reddest of the reds. Only the most intense shades qualify.
The Tosfos Yom Tov brings a beautiful Rambam on this. The Rambam writes that Hashem said regarding tumas begadim "yerakrak o adamdam", and explains that the structure of the holy tongue wastes nothing. When the Torah doubles letters in a word, that repetition is there to convey intensity, to tell us that we are dealing with something in its strongest form. Adamdam is therefore not merely red but an intense red, and yerakrak an intense green.
The word adamdam is not new to us. It came up already in the opening mishnayos of this masechta, where the Mishnah discusses pasuach, white blended together with red. The red spoken of there is likewise red at its sharpest. So too here: a red at full strength and a green at full strength.
When the color of the pisayon differs from the nega
The mishnah now takes up a case: "hayah yerakrak kegris", the nega was yerakrak the size of a gris. The Rav notes something basic here, that a gris serves as the standard measure throughout the laws of nega'im; the mefarshim explain it as a binyan av, a common denominator for nega'im generally.
The mishnah goes on: "ulesof shavua pasah adamdam", when the week came to an end, the new area that appeared beside the green was red. (Pisayon can only be spoken of once at least one week of hesger has passed.) Here the om, the nega as it first presented itself, was green, while the fresh area growing out of it was red. The mishnah then presents the opposite arrangement: the om measured a gris and was red, "upasah yerakrak", and the area that emerged from it was green. Either way the verdict is tamei. Although the added portion is wholly of the second color, it is nonetheless counted as an outgrowth of the first nega, and it functions as pisayon.
When the nega itself changes color
The mishnah's next words are "nishtanah upasah, nishtanah velo pasah, ke'ilu lo nishtanah", it changed and spread, or it changed and did not spread, it is treated as though it had not changed at all, and it is tamei.
The Rav gives a case: at the outset the nega was yerakrak and measured a gris, and by week's end it had spread out to the dimensions of a sela, a good deal wider, and at that point "bein ha'om uvein hapisayon", the first spot along with the fresh growth, are all red. One girsa printed below reads "kulo adamdam", meaning that the whole area, om and pisayon together, turned red; the second girsa amounts to the same thing, that both the om and its spreading have taken on the new color.
Here is the chiddush. In the earlier case only the pisayon was of the other color, so it was easy enough to see it as a spreading of the original nega. But now the om itself has changed as well, so that the entire nega is red where it had been green. One might have supposed that we are looking at an altogether new nega. The Tanna Kamma teaches otherwise: the change is of no consequence, and we treat the matter as if nothing had changed. If it changed and spread, the pisayon is a valid siman after the week of hesger and the person is muchlat. If it changed and did not spread, the change alone accomplishes nothing and the nega stands where it stood, requiring further hesger.
"Rebbe Yehudah omer, yeira'eh bit'chilah", Rebbe Yehudah holds that when the whole of what is now present is a different color, it is to be viewed afresh, as a nega examined for the first time. Whether it spread or not, whether it is a gris of red where there had been a gris of green, or a sela of red where there had been a gris of green, for Rebbe Yehudah this is not a continuation of the old nega at all but a new one.
As for the ruling, we do not follow Rebbe Yehudah; the position of the Tanna Kamma is accepted. A shift in color, whether the nega stays as it is or grows larger, does not sever it from its history; it remains the very same nega it was before.