Cashering Glass Utensils

In the Journal of Halacha and Contemporay Society, Rabbi Howard Jachter of Teaneck addresses the various opinions re: the Kashering of Glass. (See Number XXVI p.77)

He cites 3 Talmudic Sources:

1) Avot Debrabbi Natan {a pimarily Aggadic Work} 41:6 which states that glass neither absorbs nor exudes.
2) The Babylonian Talmud Shabbat 15b that Glass absorbs Tum'a {ritual impurity} [Reish Lakish states that Rabbanan made glass like pottery]
3) The BT Avoda Zara 75b that essentially compares glass to metal re: Tum'a and Kashrut

He then brings 4 schools amongst the Rishonim:
1) Essentially the same as ADRN above #1 that glass neither absorbs nor exudes. Ergo glass need NOT be Kashered.
2) That glass is just like earthenware - based upon Shabbat 15b for purposes of Tum'ah AND kashrut. [They apparently dismiss ADRN as Aggadic in nature and therefore not authoritative.] Ergo glass may NOT be kashered.
3) Glass is equated to metal - based upon AZ 75b. Ergo glass has the SAME parameters as metal, it CAN be cashered but may require real heat.
4) Glass is unkown, it is doubtful metal or earthenware . Ergo, in case of doubt, default to #2.

Sources in Rishonim:
#1 Tosafot, Ran, Rashba
#2 Rabbeinu Yechiel of Paris, cited by the Mordechai, the Smag
#3 Or Zarua, Ritva
#4 Rabbeinu Yona

NB: ironicallly re: #2 it is the same Ri of Paris that dismisses Kitniyyot as silly. What Ri of Paris giveth with kitniyyot he taketh away with glass!

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Cashering Glass - Talmud Shabbat 15b

Translation follows Artscroll:

As regards Glassware, what is the reason that the Rabbis decreed it is susceptible to Tum'ah? - Rabbi Yohanan said in the name of Raish Lakish: Since its very formation is from sand, the Rabbis placed it in the same category as earthenware!

NB: This is consistent with the well-known pattern that Ashkenazic practice often follows the Israeli customs - often articulated by R. Yohanan and Resh Lakish - even despite cases when Babylonian traditions might quibble otherwise.

Is Ashkenazic Tradition simply being stringent re: Glass or is it being loyal to the customs and traditions rooted in our Holy Land?!

Or is the stringency have to do more with the Passover, and not with Kashrut in general? IOW, are strictures based upon the fact that for 8.5 days it is better to be strict in the case of competing Talmudic passages since this is like a "davar sheyish lo matirim"? I.e. that since in just a few days it will be permitted, it is prohibited in the meantime?

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Cashering Glass - Avodah Zara 33b

There is a discussion re: Kunya.

1. There is an Amoraic debate between the R. Zvid and Mereimar
2. There is a definitional debate between Rashi and Tosafot as to what a kunya is
3. There is a bit of debate as to the translation of Tosafot betwen Artscroll and my own read.
4. The conclusion of the Sugya is a bit vague but it DOES suggest - at least in theory - that there a is bigger humra re: Passover - d'oraita , and Yayain Nesech derabban {what we call "stam Yanam"}

On the way to its conclusion the Talmud dismisses the cases of cracked Kunya, and regarding green ones they are slam-dunk not casherable.

The Talmud then asks your question should be regarding SMOOTH ones {D'shiyi}
The Reply of the Talmud is - as per Artscroll -
I see even that these glazed vessels sweat and since they sweat they certainly absorb thus they are fobidden {i.e. they cannot be purged}

Thus SMOOTHNESS is ruled out in the case of glazed vessels that sweat!

Note: going back to Rabbeinu Hannanel in Pesahin 74b, he defines Shiyi or Shiya in the context of there as SMOOTH but as Satum - CLOSED.

The final ruling according to Mereimar is determinative by temperature. I.e. hot glazed vessels ARE a problem while cold ones are not.

If Kunya is equivalent to glass {shiya etc.} Then:

1. It would seem to me that if you have glass that stores pure Hametz liquor or beer over 24 hours that you have a problem of kavush with regard to Passover.
2. OTOH, plain old cold glass that is not used for hot coffee, etc. should pose no such problem - if you carry the analogy of Kunya over to glass.

In my course of discussing cashering glass for Passover I recall something to the effect that glass used ONLY for cold was "Casherable" as is but otherwise it would require special handling, etc.

Kol Tuv,
RRW