פירוש על עבודה זרה 66:16

The previous baraita ruled that if a Jew buys used earthenware wine bottles from an idolater, he may put brine and murias in them. Here the Talmud asks whether the baraita meant that if he put brine and murias into them, the brine is not ex post facto prohibited, but that he should not do so. Or is he completely allowed to do so. R. Zevid’s baraita states even more clearly that he is allowed to put in the brine “ab initio” or “lechatchila” in Hebrew.

One can kasher earthenware wine vessels belonging to non-Jews by putting them back into the furnace. The heat will burn out any of the prohibited substance. R. Ashi adds that even if the pitch covering the inside of the vessel was only loosened and did not fall off, it is still permitted.

The amoraim debate whether instead of putting the earthenware jugs into the furnace (which probably could damage them), he can put lighted chips into the jugs and heat them up from the inside.
The final ruling is that this is not a valid means of kashering the jug.

According to Rava, the beer put in these wine jugs will nullify the taste of the wine and therefore it is permitted. According to R. Nahman and R. Judah it does not. As someone who knows quite a bit about beer, I must say that R. Nahman and R. Judah are usually correct. This is why some beer is allowed to age in wine barrels. It enriches the taste.

Ravina follows Rava and therefore he ruled that R. Hiyya could actually put beer into these vessels. R. Hiyya got confused and put wine in there. Rava was not concerned that by allowing people to use these vessels for beer, they would come to use them for wine. This case was just an accident.

Oops—filling the vessels with water was a good idea. Leaving them out in the sun, not such a good idea. R. Abba—maybe you could have had a bit more sympathy for R. Yitzchak?

Natron seems to be sodium carbonate. It was mined in places that also had alum. Vessels made of this material cannot be kashered for they would dissipate in water.

Since these wine vessels were not used that much, they may be simply rinsed with water and thereby koshered.

When it is first used, the cup will absorb more of the taste of the wine placed in it. That is why there is a tendency here to agree that if the first usage, or maybe even the second usage, was with forbidden wine, the it is prohibited. But if a Jew uses it the first time, or the first two times, then the cup will absorb the permitted wine. Upon further use it will no longer absorb and therefore it is permitted.

If a vessel is made in a way that it will not absorb the taste of the wine, then it need not be kashered. It can be rinsed out and used immediately.

White and black glazed vessels do not absorb the taste of the wine, but the green one’s might, so they are prohibited. And cracks will let the taste go into the vessel, so they are prohibited.

This whole section is an extended difficulty on Meremar, a late Babylonian sage. Meremar allowed all glazed vessels that had been used with non-Jewish wine. He seemed to think that such vessels do not absorb. But when it came to vessels that had been used with hametz before Pesah, he ruled much more strictly, prohibiting all of them. He saw that they “sweat,” meaning they emit liquid when heated, and therefore he assumed that they also absorb. And once an earthenware vessel has absorbed taste, there is no way to “kasher” it.