Rabbi Aryeh Lebowitz

You hear people sometimes make sweeping statements about glass, about plastic, and porcelain, and pyrex.

So maybe just to go through material by material, what can be kashrut, what cannot be kashrut, from a Pesach perspective, from an all-year-round perspective.

So one thing is clear, when the Torah talks about Adalas Kehlim in Sefer B'midbar, it talks about metal Kehlim.

So obviously metal can be kashrut.

That's a pasuk.

So that we don't need to discuss very much.

The Pasukin Vayikra, Parikha Pasuk Vav, tells us, that when you cook kadshim, when you cook a karban, in a kli keres, you have no choice but to break that kli.

Because any blia of a karban that's in a kli, at some point, is going to become nosar.

Once the Zman Achila for that Karban runs out, the Blios in the Kli are Nosar and they therefore become Asar.

And apparently, there's no way to kasher the Kli.

The only Tikkun you have for the Kli is Shvira.

And the Gemara explains that the basis for the reason for this is...

that klicheres have the capacity to be bolea, they can absorb flavor, they can even expel flavor, but you can never be guaranteed that you've gotten all of the flavor out of a klicheres.

So even if you did agala on the klicheres a hundred times, but it could be the next time you cook in that klicheres, there is still some more blios that are going to come out and are going to impact your food.

However, there is one type of kashring that works for everything, and that is libel chamor, that if you do a real kashring,

direct fire type of kashring that should work on klicharas as well.

However, Chazalberg goes that we don't do that on klicharas because we're afraid that a person is not going to do a proper kind of libon since the klicharas could break under such intense heat pressure.

I wonder if we should make a similar gezerah with self-cleaning ovens.

I've found in recent years, based on the shaylas that I'm getting, that when people self-clean their oven, the oven tends to self-destruct.

and the repairmen get very, very busy.