Chemiker wrote on Fri, 06 Feb 2009 09:51:55 -0600:

>> In article >,
>> (ms. tonya) wrote:

>> Pyrex is not supposed to be used on top of the stove and/or
>> over direct heat. See
>> this: <http://www.pyrexware.com/index.asp?pageId=104 Hmmm, I DO
>> still have my Pyrex glass double boiler for use on a
>> stovetop. I wonder why that was okay for that use. Might
>> have to look into that.
>>
>> Corningware used to be made of something called "pyroceram,"
>> and they used to make a line of stove-top-safe saucepans and
>> skillets, IIRC. http://www.epinions.com/content_4704804996

> IIRC, Pyrex owes its reputation for durability to its lower
> level of expansion under heat. Old glass was so-called
> soda-lime glass, and expanded easily under heat, which was
> self-destructive. The addition of borosilicate salts to raw
> glass lowered the coef. of expansion, which made the glass
> more resistant to thermal shock. It still has limits. I think
> Fire-king and Pyrex are about equivalent. Kimble glass calls
> their product Kimax.

> Corningware is a different breed of cat. It is fired at
> ungodly high temps and acts more like porcelain. It is
> thermally VERY stable and can take thermal shocks that would
> cause Pyrex to shatter.

Corningware, or Pyroceram, is a partially crystallized glass and, as you
say, will take themal shock. It does not bounce any better than glass or
porcelain and can break up spectacularly!


--

James Silverton
Potomac, Maryland

Email, with obvious alterations: not.jim.silverton.at.verizon.not