Before us is the thirtieth and final chapter of the tractate, and we begin with Mishnah 1. This chapter deals with the special laws governing glass vessels.
The tumah of glass vessels is rabbinic:
As has been mentioned several times in the course of our study, the tumah of glass vessels is only rabbinic. The Sages reasoned that since glass is made from sand, it is essentially close to earthenware vessels - vessels made of porcelain and ceramic - and therefore they gave it, to a certain extent, the law of earthenware vessels.
The difference between earthenware and glass:
An earthenware vessel does not become tamei from its outer surface: if a sheretz touched the outside of an earthenware jug, the jug does not become tamei, and it becomes tamei only when the sheretz is inside its inner airspace. With glass vessels the law is different, because glass is transparent, and therefore the back of the vessel - its outer surface - is considered to a certain extent like its inside. For this reason glass vessels become tamei, albeit rabbinically, even when the source of tumah, a sheretz for example, touches only their outer surface.
The general rule at the opening of the Mishnah:
The Mishnah opens with a rule we have already seen twice - at the beginning of chapter 2 and at the beginning of chapter 15 - and now it is taught again:
"Kelei zechuchis peshuteihen tehorin" - a flat piece of glass that has no receptacle and cannot hold anything does not become tamei.
"U'mekabeleihen temei'in" - glass vessels that can hold something, bowls, jugs and bottles, do become tamei.
"Nishberu taharu" - a tamei glass vessel that shattered into fragments becomes tahor. Similarly, the fragments of a glass vessel that is not tamei do not become tamei - very much like the law of earthenware vessels.
"Chazar v'asa'an kelim mekablin tumah mikan u'lehaba" - if a person took the broken fragments and restored them to their original state, or made from them a new vessel - a bowl, a bottle or a cup - this is a new vessel, which becomes tamei only from this point onward, while the old tumah has already departed from it.
The tavlah and the iskutla:
"Ha'tavlah v'ha'iskutla shel zechuchis" - the tavlah (from the word tablet) is a flat tray made of glass, and the iskutla is likewise a flat utensil, a sort of serving plate. The essential point is that they have no receptacle, except that at the bottom of the iskutla there is a small depression that serves as a kind of receptacle. It is worth noting that with wooden vessels, such an iskutla would become tamei - even though the upper surface is flat, because underneath it there is a hollow made to serve as a receptacle. But with glass vessels, whose law is like that of earthenware vessels, they do not become tamei, since the main surface is flat and the primary use is made of it.
"V'im yesh lahen lizbez temei'in" - if the tavlah or the iskutla has a rim around it, a sort of frame encircling it, they do become tamei, since now they have an inside and an interior.
The base of a bowl and the base of an iskutla:
"Shulei ke'arah v'shulei iskutla shel zechuchis" - a glass tray or flat plate that has a small depression or groove underneath, so that when turned over it can serve as a receptacle. If a person took the bottom of a glass vessel that had broken and came to use the slight depression in it as a receptacle - "af al pi shehizkinan l'tashmish, tehorin" - they do not become tamei, because the bottom of a broken glass vessel is not fit for use: its edges scratch, and whoever uses it is liable to be cut. Even though he turned the fragment over and revealed a small groove in which something could be placed, this is not a functional use, since the shards of glass injure anyone who handles them.
"Kirtison o chafon bashufin, temei'im" - if he took a substance that smooths the rough, sharp edges of the glass, or rubbed them with a filing tool and smoothed out the edges of the fragment, so that the rim and the small receptacle at its base can now be used - they do become tamei, since he has made them into a usable receptacle.
In summary: In this Mishnah we learned that the tumah of glass vessels is rabbinic, because of their similarity to earthenware vessels, except that on account of their transparency they become tamei even from their outer side. We clarified the rule that flat glass items are tahor while receptacles are tamei, that they become tahor when broken and take on tumah again once they are made into vessels; that a table and an iskutla are not tamei unless they have a raised rim; and that the bottoms of broken vessels are not tamei until their edges have been smoothed and they have become fit for use.
With this we have opened chapter 30 and completed its first Mishnah.