The Confused Image of Glass

In common years, Parshas Tzav falls on Shabbos Hagadol, and the piyutim (and perhaps the drosha) of the day teach about kashering for Pesach. Although this year is a leap year and Shabbos Hagadol is a month from now…

Question #1: Tevilas keilim

Why is glass the only material other than metal for which Chazal required immersion?

Question #2: Non-Kosher

May I use a non-kosher drinking glass for a hot cup of tea?

Question #3: Chicken soup and milk

After serving chicken soup in a glass, may I pour hot milk into the same glass?

Question #4: Kashering for Pesach

How do I kasher my chometz-dik glasses for Pesach?

Introduction

Moshe Rabbeinu hid the Egyptian that he killed in the sand; for this reason, striking the earth to bring the makeh of kinnim needed to be performed by Aharon (Rashi, Shemos 8:12). Since the world has huge deposits of sand, mankind attempted to use it for useful items, eventually discovering that, by heating sand to a very high temperature, it can be made into glassware, which is the topic of this article.

There is no mention of glassware in the Torah, although there is one reference to glassware in Tanach, in the book of Iyov (28:17). Iyov declares, regarding wisdom, lo ya’archena zahav uzechuchis, “Gold and glass do not equal it,” meaning that the value of gold or glass comes nowhere near that of wisdom. From this passage we see that, at the time of Tanach, glass was considered an extremely expensive material. As we will see shortly, that glass became less costly with time has halachic ramifications.

Before discussing the halachos of glass, let us note some of its unique chemical and physical properties that affect its halachic status.

Recyclable

Glassware has many uses and can be very beautiful, but at the same time it is fragile and breakable. However, as opposed to pottery, which, when broken, is irreparable and virtually useless, broken glassware can be easily recycled. Glass can be melted down and reused over and over. In this respect, glass shares an important characteristic with metals, which are also recyclable by being melted down. For this reason, Chazal sometimes gave glassware the halachos of metals. For example, germane to the mitzvah of tevilas keilim, the Gemara rules that glass vessels must be toiveled before use, as indicated in the Gemara (Avodah Zarah 75b): Rav Ashi said, Glass utensils, since when broken they can be repaired, are like metal utensils.

Rav Ashi lived at the very end of the period of the Gemara. A much earlier statement of Chazal, in Avos deRabbi Nosson (Chapter 41), provides the following terse statement:

“Three things were said regarding glassware:

(1) It does not absorb; it does not impart.

(2) It shows whatever is inside.

(3) If you place it in a hot place, it becomes hot. If you place it in a cold place, it becomes cold.”

Avos deRabbi Nosson is not intended to be a scientific work, nor is it a handbook for manufacturers. It is similar to Pirkei Avos, although it contains much more aggaddic material, and so it would probably be best classified as an early midrash, similar to Midrash Tanchuma or Pirkei deRabbi Eliezer, or to the much later midrashic collections like Midrash Rabbah or Yalkut Shimoni. So, why is it concerned with categorizing the qualities of glassware?

The answer to this question is that, although Avos deRabbi Nosson is not usually treated as a halachic midrash, in this instance, that is exactly what it is — providing halachic categorization with which to define the unique qualities of glass. By so doing, it provides a background with which to explain the halachos of glassware.

Does not absorb

Laboratory experiments use glass equipment because it does not absorb, nor does it impart or leach into what is heated or stored inside it. Therefore, it should not affect whatever chemical reaction or research for which it is being used. We will soon discuss the kashrus ramifications of this quality of glass, about which the Avos deRabbi Nosson was presumably concerned.

May be clear or opaque

We are accustomed to most glass being clear, but this is really a function of what other chemicals are in the sand from which the glass is made when it is fired. Even glass that is colored is usually transparent, which is one of the common qualities of glass and is highly uncommon in other materials.

This observation about glassware has much halachic ramification, although this distinction does not affect any “kitchen kashrus” issues. It does, however, have ramifications for the laws of tumah and taharah, which we will not disuss in this article because of space considerations.

It is a conductor

The third statement of the Avos deRabbi Nosson is that if you place glass in a hot place, it becomes hot, and if you place it in a cold place, it becomes cold. In other words, glass is a conductor and not a good insulator. The best insulator used today in the kitchen and in carryout shops is Styrofoam. But on the relative scale of things, glass is closer to metal in its ability to conduct heat.

Having used the Avos deRabbi Nosson as a means of explaining the unique properties of glass, we can now discuss the halachic questions that I raised at the beginning of our article.

Tevilas keilim

Our first question was: Why is glass the only material other than metal for which Chazal required immersion?

Allow me to explain. The laws of tumah and taharah germane to tools, equipment and vessels include many different types of materials. Items manufactured from metal, wood, cloth, horn, glass, and plants are all susceptible to tumah, as is food, pottery and boneware. Nonetheless, germane to the mitzvah of immersing utensils prior to food use, the requirement min haTorah  applies only to metal utensils, and not to utensils, pots or pans made of pottery, wood, cloth, bone, horn or any other materials. Therefore, there is no requirement to toivel a wooden spoon, a ceramic dish, cheesecloth used for food (after all, it is called cheesecloth, and not laundry cloth, for a good reason), or flatware chiseled out of horn or bone. However, why is there a requirement to toivel glass bowls and cups?

Based on the Gemara that we quoted above, we can answer this question: Broken glass utensils can be recycled for new manufacture, just as you can recycle broken metal utensils. Since glass shares this quality with metal, Chazal instituted that glass be treated like metalware, germane to the mitzvah of toiveling food-preparatory vessels prior to using them.

Glass and kashrus

At this point, I am going to combine the next three of our opening questions into one discussion:

May I use a non-kosher drinking glass for a hot cup of tea?

After serving chicken soup in a glass, may I pour hot milk into the same glass?

How do I kasher my chometz-dik glasses for Pesach?

There is a tremendous diversity of opinion among the rishonim concerning the kashrus status of glassware. Do we assume, halachically, as does the chemist, that glass never imparts anything that it absorbs? If this is true, it should never require kashering and it may be used interchangeably from treif to kosher, from milchig to fleishig, and from chometz to Pesach without any kashering procedure at all. On the other hand, we have no Talmudic source that expressly permits using any utensil in any of these ways without a kashering procedure in between.

The different opinions that we find among the rishonim on this issue can be categorized loosely as three basic approaches:

1. No need to kasher

Several authorities contend that the nature of glass is that it does not absorb or impart any taste and that, therefore, it does not require any kashering at all (Rabbeinu Tam, quoted by Tosafos, Avodah Zarah 33b s.v. Kunya and Kesubos 107b s.v. Hani,and Rosh, Pesachim 2:8; Rashba, both in Shu”t Harashba 1:233 and in Toras Habayis 5:6; Ran, Pesachim 9a [in the Rif’s pages]; Ravyah,quoted by Mordechai, Pesachim #574). Many of these authorities quote the above mentioned Avos deRabbi Nosson as a proof for this ruling.

2. Does not help to kasher

Halacha treats glassware like pottery. Once pottery was used to cook chometz or non-kosher food, the flavor absorbed into its walls can never be fully removed. Rather than becoming completely extracted when one attempts to kasher pottery, some of the absorbed taste remains and leaches out afterwards with each use, potentially spreading prohibited flavor into all subsequent cooking (Tosafos, Chullin 8a s.v. Shelivna). In other words, once pottery becomes treif, it may be impossible to make kosher again. (There are some circumstances in which it can be kashered, but these unusual situations are beyond the scope of this article.)

Some early authorities contend that, since glassware is made from sand, it should be treated like sand, or, more accurately, like pottery and cannot be kashered (Mordechai, Pesachim #574, and Avodah Zarah #826; Terumas Hadeshen 1:132, 2:151). Most of these authorities quote the source for this approach as Rabbeinu Yechiel of Paris, one of the baalei Tosafos.

3. Glass is like metal

Some rishonim rule that just as Chazal gave glassware the same halachic status as metal regarding the mitzvah of tevilas keilim, it has the same halacha regarding the laws of kashrus (Bedek Habayis of the Re’ah, 5:6; Shibbolei Haleket #207).

However, once we rule that glassware is like metal, in practice, it might become stricter than metal. This is because of a rule that, when a particular method of kashering may break an appliance, Chazal prohibited using that method, out of concern that someone will be afraid to kasher it properly (Pesachim 30b). Thus, although metal can be kashered by boiling the appliance (hag’alah), it may not be allowed to kasher glassware this way, because the owner may be afraid that it will crack (Mor Uketzi’ah end of 451). On the other hand, other authorities permit kashering glassware by hag’alah for Pesach and are not concerned that someone might be afraid to kasher it properly (Shu”t Maharsham 1:53 at end).

A major halachic ramification results from the above. Glassware that is meant to be used in the oven, such as Pyrex, should, therefore, be kasherable for Pesach, since presumably the owner will not be afraid to kasher it properly. Although this is not common custom, there are prominent halachic authorities who permit this (She’arim Hametzuyanim Bahalacha 116:11).

Difference between treif and Pesach

There is a dispute among rishonim whether glass that was used for hot chometz may be used for Pesach. Some authorities are more stringent regarding using chometz-dik glassware for Pesach than using it interchangeably between milchig and fleishig. For example, the Hagahos Semaq, a late baal Tosafos, writes: “Universal custom is not to use for Pesach any used pottery vessels (even those coated with metal or glass). Rabbeinu Yechiel prohibited using even used drinking glasses, since the Gemara compares glass to pottery, and sometimes people place bread into drinking glasses, in which instance they absorb the way pottery does.” The way this statement is quoted, it implies that Rabbeinu Yechiel did not permit any form of glassware kashering for Pesach (Hagahos Semaq 222:5).

Similarly, the Issur Vaheter (58:50), an early Ashkenazic posek, quotes the Semaq as ruling that it is prohibited to kasher glass for Pesach and it should be treated lechumra as questionable whether it is considered metal or pottery.

How do we rule?

Among earlier halachic authorities, it appears that there was a big difference between Sefardic and Ashkenazic practice regarding the use of glassware. The Beis Yosef cites most of the halachic sources we quoted above, and concludes, both in Beis Yosef and in Shulchan Aruch, that glassware does not absorb and therefore may be used for Pesach without any kashering procedure at all (Shulchan Aruch, Orach Chayim 451:26). Following his approach, it would appear that someone could purchase or rent used glass equipment from a treif source, without any need to kasher it.

On the other hand, early Ashkenazic custom appears to have been closer to the approach of Rabbeinu Yechiel cited above. For example, the Rema rules that chometz-dik glassware should not be used for Pesach and that it is not kasherable for Pesach use, even when it was used only for serving cold beverages and not used ever to store them.

Although most Ashkenazic authorities subsequent to the Rema follow his approach, some rule that Ashkenazim could follow the Sefardic practice and use glassware for Pesach without kashering it first (Mor Uketzi’ah,end of 451).

Other authorities raise a different question regarding the Rema’s ruling that glassware may not be used for Pesach. The Rema prohibits using glassware for cold drinks on Pesach, even when the glass is used only for cold beverages the entire year. The reason the Rema is stringent is because of concern that chometz may have fallen into the glass and became kavush, which means that chometz flavor absorbed into the glass.

The difficulty with this ruling is that the Rema himself rules that a vessel, even made of pottery, that stored chometz for a lengthy period of time may be used on Pesach, even when this long-term storage would create kavush (Orach Chayim 451:21; see Mishnah Berurah 451:122). How could the Rema treat glassware more stringently than pottery? The only reason to be stringent regarding glassware is according to the minority opinion that treats glassware as pottery!

This question is raised by the commentary Beis Meir (Orach Chayim 451:26), who answers that the Ashkenazic minhag to be stringent not to kasher glass was only regarding drinking glasses, since buying new ones for Pesach is not a major expense. However, the Rema ruled leniently regarding large storage vessels that are expensive, even when they are made from pottery, and certainly when they were manufactured from glass. In other words, even the Rema holds that glassware is inherently kasherable; there is only a custom not to kasher drinking glasses for Pesach since this does not incur a great expense.

There are several ramifications of the Beis Meir’s ruling:

An individual who cannot afford to purchase glassware for Pesach may use his regular, chometz-dik glassware. In this situation, he should kasher his drinking glasses. This approach is followed by the Chayei Odom and the Mishnah Berurah (451:156) who rule that, in a place where glassware is relatively unavailable, glass items should be cleaned well and then kashered for Pesach, by a method called miluy ve’iruy. In this kashering method, glasses are submerged completely in a basin or tub full of cold water for at least 24 hours, the water is changed and glasses are submerged again for at least another 24 hours, and then a third time for at least another 24 hours.

The Mishnah Berurah rules that, if someone does not ordinarily use his glassware for hot chometz or to store chometz, and they used their glasses for Pesach without any kashering at all, the food or beverage placed in them remains kosher for Pesach. More so, in a case of major loss, the Mishnah Berurah permits Pesach-dik food, even when it was placed hot into glassware that was previously used for hot chometz. He permits this only if the glassware was not used for chometz within the previous 24 hours. There are other authorities who are even more lenient (Taz; Pri Chodosh; cf. Shaar Hatziyun 451:196).

According to the Beis Meir’s conclusion, it is permitted to drink a kosher beverage, even a hot tea or coffee, in a “non-kosher” drinking glass. This opinion is mentioned by many halachic authorities (Keneses Hagedolah, Yoreh Deah 121:25 in Hagahos Tur 25; Darkei Teshuvah 121:2; Aruch Hashulchan, Yoreh Deah 121:2). Thus, if you are in a non-kosher house or hotel, the hot tea or coffee you are served in a glass is still kosher. And, if we refer to one of our opening questions: “After serving chicken soup in a glass, may I pour hot milk into the same glass?” — the answer, according to these authorities, is that one may. I suggest that, prior to putting this into practice, our readers should ask this question from their own rav or posek.

Conclusion

The Chiddushei Harim notes that pottery vessels become tamei only from their inside and not when something touches their outside. He explains that this is because a pottery vessel, itself, is considered without inherent value – its value is determined by what it contains, whereas vessels made from other materials have inherent value. On this basis, the Sfas Emes, the grandson and successor of the Chiddushei Harim, notes that man’s value is also determined by what he contains on the inside, not on his outer projected image.

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