[Avodah] Using an oven for both fleishigs and milchigs

[Micha Berger via Avodah]

On Wed, Aug 31, 2016 at 09:46:36AM +0300, Eli Turkel wrote:
: On Tue, Aug 30, 2016 at 11:17 PM, Micha Berger <micha at aishdas.org> wrote:
:> However, se'if 9 discussing cooking utensils says that keli zekhukhis ein
:> bahem tashmish bechamin. So if glass were usable as actual keli rishon
:> cookware, perhaps he would be machmir. But the AhS predated the common
:> use of pyrex and the like.

: again from Rav Heineman
:> Q: Is corningware glass?
:> A: No, it is like china.

But even though corningware and pyrex are both inventions of Corning Inc,
I would not say it is "and the like".

Pyrex is a borosilicate glass. As opposed to the usual glass,
which is sode-lime glass. Regular glass expands when heated, and is
a poor conductor of heat. So, when you heat up one side, it epands
diginicantly faster than the rest, and as a result, your keli shatters. By
replacing sodium with boron in the formula, they lower the expansion
coefficient. The resulting keli therefore doesn't shatter when heated,
and is therefore usable for beakers to be placed atop bunsen burners,
or pots to be placed on stoves or ovens. It really is glass, a non-porous
mostly melted-silicon thing.

Corningware (identical to Europe's "Pyroflam") is a glass-ceramic.
Meaning, it glass that is reheated and parts are allowed to crystallize.
A different resulting structure than actual glass.

Arguing that corningware is partly ceramic and therefore a keli cheres
is much simpler. And then one gets into the question as to whether one
should treat a non-porous keli cheres like other cheres. A question
resolved lechumera earlier, with porcelain.

Tir'u baTov!
-Micha

-- 
Micha Berger             When we are no longer able to change a situation
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