Borosilicate glass -- easy fracture?

I was under the impression -- perhaps false -- that "Pyrex" and other borosilicate glasses didn't fracture as easily as natural untempered
glasses, but a light impact resulting in a very sharp concoidal sliver from the inside rim of one "ovenware" top that we have made me think again. Isn't most "ovenware" tempered? I know tempering is an entirely separate consideration from composition, but are untempered borosilicates any more or less apt to fracture or shatter than regular glass?
TIA Mark 'Sporky' Stapleton Watermark Design, LLC www.h2omarkdesign.com
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On Tue, 28 Jun 2005 16:28:52 -0400, Sporkman

Because Pyrex has a low thermal expansion coefficient, it can't really be thermally toughened, but chemical toughening is feasible.
If you break, or chip, a toughened article you will end up with a pile of glass granules. Your Pyrex vessel will remain largely intact unless you have a major fracture.
--
Terry Harper
URL: http://www.terry.harper.btinternet.com /
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Terry Harper wrote:

--------------------- Thanks to you and Uncle Al for your replies. (And BTW, your link doesn't seem to work.)
Your comments make me suspect even more strongly that perhaps the "ovenware" wasn't high quality, or perhaps wasn't even borosilicate at all. It was the slightest of impacts against another piece of ovenware that brought at 3" long and very skinny (and VERY sharp) shard off of the inside rim of the top cover.
'Sporky'
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On Tue, 28 Jun 2005 22:29:49 -0400, Sporkman

Pyrex will chip in the way that you describe. I've also broken pyroceram vessels by dropping them, but usually only two pieces resulted.
Thanks for the comment about the link. It seems to be a whim of BTinternet.
http://www.btinternet.com/~terry.harper/ should work, where I had the same problem as you just now.
--
Terry Harper
URL: http://www.terry.harper.btinternet.com /
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