Kashering Glass Utensils

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by R. Gidon Rothstein

R. Ezriel Hildesheimer Defends Kashering Glass Utensils

[Click here for the audio version].

The Torah does not mention glass as a material for utensils such as pots and pans, leaving us no instructions for how to make glass items kosher. We often assume it is impervious to absorption, which would mean we could wash it off carefully and use it (or, as many do before Pesach, could soak it in water for three consecutive days, changing the water every twenty-four hours).

The question arises again regarding glazing, where a thin layer of glass is applied on top of some plate, pot, or the like. Can such glass absorb and, if yes, can it be koshered?

The Original Article’s Support of Kashering

Much of Shu”t R. Ezriel Hildesheimer 1; Orach Chayyim 69, dated 16 Tammuz 5625 (1865), records the complaints of a R. Reuven Fink about an article by a R. David Deutsch in Der Israelit [an Orthodox Jewish weekly published from 1860 until the Nazis, yemach shemam ve-zichram, outlawed it in November of 1938].

The article had cited Shulchan Aruch’s position, glass does not absorb, to permit kashering glazed pots. R. Deutsch knew Rema disagreed, but did allow koshering glass bedi’avad, after the fact, because Shulchan Aruch fundamentally required us to treat a glaze like clay, which cannot be koshered. In our days, R. Deutsch had said, we treat all pots and pans as bedi’avad (he does not explain why, and I’m not familiar with the source).

Glaze is Not the Same as Glass

R. Deutsch relied on Rosh as the source of the distinction between glass and glazed utensils. R. Fink expresses surprise he failed to note Tosafot Ketubbot 107b, which already makes the distinction, but with a difference which R. Fink thinks refutes his leniency. Tosafot said glazes are not fully cooked (since the glass is not going to be a free-standing item, it does not need as much solidity, which leaves it halachically equivalent to clay, and therefore permeable).

Not fully cooked clay (which is how glass starts out, halachically) cannot be kashered, since clay never fully releases what it absorbs (from an halachic perspective). Even authorities who permit kashering regular glass pots or pans, such as Magen Avraham or Darkei Moshe, might concede here, because the glaze is more like clay than a fully glass utensil.

Once we see Tosafot’s version, we have to consider the possibility Shulchan Aruch based his view on Rosh, which takes away the possible leniency of treating glazed pots or pans as bedi’avad, and allowing us to kasher them, as we would regular glass utensils.

The Role of the Underlying Material

R. Deutsch also pointed to Avodah Zarah 33, where Maharsha said glass-glazed clay (such as glazed china) cannot be kashered, because the glaze is the same type of material as the clay. While it changed and acquired different properties to become glass, Maharsha thought attaching it to clay returned it to principles of absorption and koshering relevant to clay. Maharsha’s focus on the underlying clay supports R. Deutsch’s assessment of glaze on other materials, meaning we should either not need to kasher them, or should be able to.

R. Fink apologizes ahead of time for his audacity in challenging Maharsha, but thinks Tosafot Ketubbot negates Maharsha’s view. Tosafot Avodah Zarah does on its own convey the messages Maharsha inferred. But Tosafot Avodah Zarah also mentions the idea of fully cooked, which tells R. Fink it is hinting at the actual main concern, the one Tosafot Ketubbot makes clear, whether or not the glaze was a fully worked out material.

He admits Tosafot Avodah Zarah spoke of the glass as being only a chipui, a cover, support for Maharsha’s reading, but thinks it’s too flimsy to establish a dispute between the two passages in Tosafot (we do recognize times when Tosafot takes different positions in different tractates, since Tosafot is a compilation of many rabbis’ views; R. Fink thinks we need more clear a difference before we say there’s a hitherto unrecognized disagreement).

Sum total, he thinks there’s insufficient support for the leniency presented in Der Israelit, that glass-glazed metal pots and pans can be kashered.

R. Hildesheimer Defends R. Deutsch

R. Fink did not notice the uniformity of Tosafot in referring everywhere only to a clay utensil, which led Maharsha to his reading. The Aruch, too, referred only to glaze on clay, as does Shulchan Aruch and all who codify these laws. To R. Hildesheimer, this means the sources R. Fink thought supported him actually ends up hurting his claim.

(R. Hildesheimer expresses that by quoting Yeshayahu 31;3, which warned against relying on Egypt too much, since ve-kashal ‘ozer ve-nafal azur, when the supporter fails, the one supported will fall fully. In the original context, it was about the Jews’ reliance on Egypt to protect them from other invaders; when Egypt left the picture, they’d have nothing, since they failed to rely on Hashem. R. Hildesheimer is saying R. Fink, too, built his case on Tosafot in Ketubbot; as soon as R. Hildesheimer shows he’s misread Tosafot’s implication, his argument falls. It as an example of a common rabbinic technique, applying verses or sayings from one context aptly to another).

We still do have to address Tosafot’s distinction between glass and glaze. R. Hildesheimer notes Tosafot speaks first about completed glass and then adds glaze does absorb “and more so.” Why “more so?” R. Hildesheimer suggests it’s to alert us to glaze’s being fully permeable, it absorbs and also releases what’s absorbed.

Were there an item of all glaze [which is impossible by definition, but he’s making a point], it would be kasher-able, since it just absorbs and releases. When it’s an overlay of another item, the underlying material becomes important. On a clay utensil, it will absorb and deposit taste into the clay, which will then never fully release and cannot be kashered.

For R. Hildesheimer, glaze is an in-between stage from clay (which never fully releases what it has absorbed) and glass (which never absorbs). Glaze absorbs and releases, and therefore can or cannot be kashered depending on the material on which its applied.

Cooking in Only One Spot

The very last bit of the responsum argues about whether one would have to kasher an entire pot if we know the non-kosher material hit only one area. R. Fink claimedTerumat HaDeshen allowed spot-kashering only when the problem was created by ‘irui, pouring hot non-kosher material onto a certain spot (the extent to which ‘irui transfers taste is itself a matter of debate); for full cooking (even if in a very restricted location), R. Fink thought a full kashering was the obvious requirement.

R. Hildesheimer concedes Magen Avraham presented the issue as R. Fink did, but thought the responsum of Terumat HaDeshen itself said something different. Terumat HaDeshen quoted Semag, who thought we have to see cooking as affecting a whole item only in kodashim, issues of sacrifices.

He closes with thanks for R. Fink copying out R. Akiva Eiger’s language in his glosses to Orach Chayyim, since he does not own the book [I am always curious and interested about the libraries with which great Torah scholars worked; for all the scholars known for their astonishingly encyclopedic knowledge, we have other greats who worked with what they had, tilling, planting, and reaping much in the world of Torah].

He is surprised R. Akiva Eiger did not comment on the difference between the original responsum and how Magen Avraham recorded it [he does not imagine R. Akiva Eiger did not have access to the original; R. Hildesheimer had some academic tendencies—he founded the well-known rabbinical seminary that bore his name, where secular knowledge was a productive adjunct or aid to one’s Torah knowledge, and he edited an annotated Halachot Gedolot.

I mention his academic leanings because his comments about looking back at the original—for all they could certainly have been authored by a fully traditionalist Torah scholar– seem to me to carry a whiff of the academic interest in original sources, and awareness that those sources are not always fully and accurately represented by later versions of them].

Glazed china gets no room to be kashered in R. Hildesheimer’s discussion, but glazed metal avoids the fate R. Fink wanted, our treating the glass like clay, and turn what was once kasher-able into items with no remedy should they absorb non-kosher material.

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