Talmud - Shabbat 15b שבת ט״ו ב׳

Rather, this decree was issued in stages. First, Yosei ben Yo’ezer and Yosei ben Yoḥanan came and issued a decree that teruma that comes into contact with a clump of earth of the land of the nations is to be burned, and they decreed nothing with regard to teruma that enters into the air space of the land of the nations. The Sages of the final eighty years prior to the destruction of the Temple came and issued a decree with regard to teruma that enters into the air space of the land of the nations that its legal status is in abeyance, and it is not burned.

The Gemara asks: Is that to say that there was one decree issued immediately to subject teruma to burning? Didn’t Ilfa say: With regard to hands, from the beginning their decree was that teruma that comes into contact with them is to be burned? The Gemara infers from this that, with regard to hands alone, the beginning of their decree was to render teruma that came into contact with them impure to the point of burning; however, with regard to other matters, they did not immediately issue so severe a decree.

Rather, the stages of the decree were as follows: Yosei ben Yo’ezer and Yosei ben Yoḥanan came and decreed that any item that came into contact with a clump of earth is to be in abeyance, and they decreed nothing with regard to teruma that enters into the air space of the land of the nations. The Sages of the last eighty years came and were stringent by one more level; they decreed that teruma that came into contact with a clump of earth of the land of the nations is to be burned, and, with regard to teruma that enters into the air space of the land of the nations, its legal status is in abeyance.

The Gemara asked further: And still is the matter clear? Didn’t the Sages issue this decree in Usha, many years after the destruction of the Temple? As we learned in a mishna: For six cases of uncertain impurity one burns the teruma which came into contact with them:
For the uncertain case of beit haperas, meaning teruma that entered a field where a grave was plowed and the location of the bones of the corpse is unknown, and it is uncertain whether or not the teruma became impure;
And for the uncertain case of earth that comes from the land of the nations, whose impurity itself has the status of uncertain impurity. Therefore, teruma that came into contact with it also has the status of uncertain impurity;
And for the uncertain case of the clothes of an am ha’aretz. Since an am ha’aretz is not careful with regard to purity, we are concerned lest a menstruating woman touch his clothes. Due to that uncertainty, his clothes are considered impure with a severe degree of impurity. If teruma came into contact with them there is uncertainty with regard to whether or not they became impure;
And for the uncertain case of vessels that are not his that are found. Since he does not know whether or not those vessels are impure, if teruma came into contact with them, there is uncertainty whether or not they are impure;
And for the uncertain case of spittle, as perhaps it is the spittle of a zav and transmits impurity by Torah law. If teruma came into contact with it there is uncertainty whether or not it is impure;
And for the uncertain case of a person’s urine, even though it was adjacent to the urine of an animal, there is room for concern that perhaps it is the urine of a zav, and impure by Torah law. If teruma came into contact with it, there is uncertainty whether or not it is impure.
In all of these cases, the Sages established that for their definite contact, when it is clear that these came into contact with teruma, and although there is uncertainty with regard to their essential impurity, i.e., it is uncertain whether or not these items are impure, one burns the teruma that came into contact with them.

Rabbi Yosei says: Even in a case of uncertain contact; if it was in the private domain one burns teruma that came into contact with it, as with regard to impurity by Torah law an uncertainty that developed in a private domain is also ruled impure. According to Rabbi Yosei, these decrees, even though they are fundamentally cases of uncertainty, are sufficiently stringent that the Sages applied Torah law to them. And the Rabbis say: Since these cases are only impure by rabbinic decree, in a case of uncertain contact in the private domain, one does not burn the teruma but rather places it in abeyance. While in the public domain, they are ritually pure.

And Ulla said with regard to these six uncertain cases: In Usha they instituted how one must act in terms of practical halakha. If so, a clump of earth from the land of the nations transmits impurity from the time of the Usha ordinances and not from eighty years prior to the destruction of the Temple. Rather, Yosei ben Yo’ezer and Yosei ben Yoḥanan came and decreed that if teruma came into contact with a clump of earth from the land of the nations, its legal status is in abeyance and one does not burn it, and upon teruma that entered the air space of the land of the nations they decreed nothing. And the Sages of the last eighty years of the Temple came along and issued a decree upon this, earth, and upon that, air, that in both cases the teruma is in abeyance. And the Sages of the city of Usha came along and decreed that teruma that came into contact with a clump of earth from the land of the nations is burned. And teruma that entered the air space of the land of the nations, as it stood, it continues to stand in abeyance. They did not impose any greater stringency in this matter.

One of the matters mentioned above was the decree of impurity on glass vessels. With regard to glass vessels, what is the reason that the Sages decreed impurity upon them? Rabbi Yoḥanan said that Reish Lakish said: Since the beginning of the manufacture of glass vessels is from sand, the Sages equated them to earthenware vessels. The Gemara asks: But if what you say is so, if the Sages truly equated the impurity of glass vessels to the impurity of earthenware vessels, there should not be purification in the ritual bath for glass vessels, just as there is no purification for earthenware vessels. Why, then, did we learn in a mishna with regard to the halakhot of immersing vessels: And these materials interpose in vessels, i.e., if they were stuck to the vessel when it was immersed the vessel is not purified: The pitch and the myrrh that were stuck on glass vessels obstruct their immersion. Apparently, glass vessels are purified in a ritual bath.

The Gemara answers that glass cannot usually be purified in a ritual bath. However, with what are we dealing here? With a special case where the glass vessels were perforated and he dripped molten lead into them to seal the hole. This halakha is in accordance with the opinion of Rabbi Meir, who said: Everything follows the nature of the facilitator, i.e., if an object that is not fit for use on its own is reinforced with a different material that facilitates its use, the entire object assumes the legal status of that material. Therefore, since the substance that sealed the holes in these glass vessels is lead, which can be purified through immersion like other metals, these glass vessels can also be purified in a ritual bath. As it was taught in a baraita: Glass vessels that were perforated and one dripped lead into them; Rabban Shimon ben Gamliel said that Rabbi Meir deems them ritually impure and the Rabbis deem them ritually pure.

The Gemara asks further: But if that is so, and glass vessels are equated with earthenware vessels,

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Shabbat 15b traces the historical stages of rabbinic decrees on impurity from foreign lands, examining when teruma should be burned versus held in abeyance.