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		Chabad.org » Jewish Practice » Kosher » Handbook » Kosher Q&A » Can glass be koshered?

2 Comments Posted

Can glass be koshered?

By Menachem Posner

Whether glass can be koshered is the subject of debate among the early halachic authorities.

There are those who opine1 that glass is a completely non-porous and non-absorbent substance. As such, it never absorbs any traces of chametz or non-kosher foods, and a thorough washing of its surfaces is sufficient to make it kosher.2

On the other extreme, many authorities3 maintain that glass is to be treated like earthenware, a substance which is completely un-kosherable. According to them, there is no way to kosher glass.4

Taking the "middle ground," there are those5 who see glass as a material similar to metal,6 which can be koshered through exposure to high levels of heat.7

Ashkenazi Jewry follow the most stringent view, and do not use chametz glassware on Passover, nor do they kosher non-kosher glassware. If you are of Sephardic ancestry, consult with your rabbi regarding accepted protocol in your community.

Yours truly,

Rabbi Menachem Posner

2 Comments Posted

FOOTNOTES
1.	Ran, Rashba, Yosef Karo and others.
2.	This opinion is based on a passage found in Avot D'Rabbi Nathan (41:6) which states that "glass neither absorbs nor exudes."
3.	Smag, Rama and others.
4.	They offer alternative interpretations for the aforementioned passage from Avot D'Rabbi Nathan.
5.	Ohr Zarua and others.
6.	They deduce this from the fact that the two materials are treated with equal stringency in the Talmud, tractate Avodah Zarah 75b.
7.	For more on the koshering procedure for metal – and other similar substances – see Koshering Appliances and Utensils.

By Menachem Posner More articles... |

Rabbi Menachem Posner is a member of the chabad.org Ask the Rabbi team.

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Reader Comments
Latest Comments:

Posted: Apr 21, 2009

its a little disengenguous to say Ashkenaz Jewry doesnt kosher glassware, maye not for Pesach, but for the rest of the year, many Ashkenaz Ravs would tell you glass doesnt absorb, including those of the major Kashrus organizations. It would be more accurate to say that some Chassidim dont use "nonkosher" glass. I remember reading Rav Steinsaltz in his book about teshuva says you can just scrub your glassware clean and its Kosher although possibly he wasnt addressing Chabad Chassidim. I personally at home dont use "non kosher" glassware but that said I dont consider it halachich by Ashkenaz standards, and (based on Rav Steinsaltz) maybe not even by Chabad

Posted By Moshe

Posted: Apr 2, 2008

Glass is sometimes porous

Glass is often porous near the surface depending on what materials come into contact with the glass. For example, certain acids can render the surface porous. Even water can slowly eat holes into the surface of glass. Bases, however, eat up the whole surface of glass exposing a clean new surface layer underneath. Perhaps glass that has been in contact with chametz could be koshered by washing the surface with a base (such as lye) solution? Visit the Corning Museum of Glass online for more information.

Posted By David Goorskey, Fayetteville, AR/USA

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