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| Salmon Egg... |
 Posted: Fri Oct 02, 2009 8:26 am |
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I have heard of problems with Pyrex cookware that may be urban rumor. I
would like to get first hand information on the subject.
1. Does Corning supply Pyrex tubing and glassware to the chemistry
community? If not, who does?
2. Has Corning sold the Pyrex trademark for consumer products?
3. Does it make any sense for any new manufacturer, say in China, to
substitute soda lime glass for borosilicate glass to improve their
bottom line?
I was just sent email claiming that Pyrex brand cookware is at least
partially soda lime glass. The result is there is serious breakage in
the oven. There is such a disparity in the thermal expansion properties
of borosilicate glass and soda lime glass that I find it difficult to
believe that soda lime is ever suitable for ovenware.
That gets me to another question. What did chemists use for glass ware
before borosilicate glass? How were they able to prevent breakage of
flasks and other containers used for heating? Apparently Pasteur was
able to blow some flasks exposed to the atmosphere through undulated
tubes that trap bacteria. I understand that some of these flasks still
are in France with uncontaminated broth sterilized in the flasks well
over a hundred years ago.
Bill
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Private Profit; Public Poop! Avoid collateral windfall! |
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| dlzc... |
| Posted: Fri Oct 02, 2009 8:26 am |
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On Oct 2, 7:26 am, Salmon Egg <Salmon... at (no spam) sbcglobal.net> wrote:
[quote:189b311022]I have heard of problems with Pyrex cookware that
may be urban rumor. I would like to get first hand
information on the subject.
1. Does Corning supply Pyrex tubing and
glassware to the chemistry community? If not,
who does?
[/quote:189b311022]
http://en.wikipedia.org/wiki/Pyrex
.... this is not to say that they might not have outsourced manufacture
elsewhere...
[quote:189b311022]2. Has Corning sold the Pyrex trademark for
consumer products?
[/quote:189b311022]
No mention on Corning's website of having sold the brand.
[quote:189b311022]3. Does it make any sense for any new
manufacturer, say in China, to substitute soda
lime glass for borosilicate glass to improve their
bottom line?
[/quote:189b311022]
Corning did it.
[quote:189b311022]I was just sent email claiming that Pyrex brand
cookware is at least partially soda lime glass.
[/quote:189b311022]
Yes, see the link above.
[quote:189b311022]The result is there is serious breakage in the
oven. There is such a disparity in the thermal
expansion properties of borosilicate glass and
soda lime glass that I find it difficult to believe
that soda lime is ever suitable for ovenware.
[/quote:189b311022]
If it has been strain relieved, there should be no breakage unless
different glasses are in close mechanical contact (stopper is one
glass and flask is another glass).
My only interaction with glass is aluminosilicate and borosilicate
glass for ozone production dielectrics.
David A. Smith |
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| normfromga... |
| Posted: Tue Oct 13, 2009 4:28 am |
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Guest
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On Oct 2, 10:26 am, Salmon Egg <Salmon... at (no spam) sbcglobal.net> wrote:
[quote:997e2aa398]I have heard of problems withPyrexcookware that may be urban rumor. I
would like to get first hand information on the subject.
1. Does Corning supplyPyrextubing and glassware to the chemistry
community? If not, who does?
2. Has Corning sold thePyrextrademark for consumer products?
3. Does it make any sense for any new manufacturer, say in China, to
substitute soda lime glass for borosilicate glass to improve their
bottom line?
I was just sent email claiming thatPyrexbrand cookware is at least
partially soda lime glass. The result is there is serious breakage in
the oven. There is such a disparity in the thermal expansion properties
of borosilicate glass and soda lime glass that I find it difficult to
believe that soda lime is ever suitable for ovenware.
That gets me to another question. What did chemists use for glass ware
before borosilicate glass? How were they able to prevent breakage of
flasks and other containers used for heating? Apparently Pasteur was
able to blow some flasks exposed to the atmosphere through undulated
tubes that trap bacteria. I understand that some of these flasks still
are in France with uncontaminated broth sterilized in the flasks well
over a hundred years ago.
Bill
--
Private Profit; Public Poop! Avoid collateral windfall!
[/quote:997e2aa398]
I was somewhat surprised to get a similar e-mail, warning about the
"new" Pyrex, but not astounded; Corning had sold soda-lime juice
flasks for decades, using the Pyrex trademark, but got away with it by
simply warning the customer that it was not for stove/oven use. Once
you own a trademark, you can apply it on just about anything.
Apparently World Kitchens, who bought out the consumer division in
1998, decided that it could take this a step further, by simply
warning people, on its throw-away packaging, not to try moving the
Pyrex bakeware directly from fridge to oven, among other caveats.
For it is not the change of temperature that brings about problems
when a glass has a higher thermal expansion coefficient, but the rate
of change; if the glassware is taken from one temperature extreme to
another, without allowing it to evenly heat or cool throughout, THAT
is when things get violent.
The interesting thing is that we can’t blame this problem on the
Chinese, which was portrayed the culprit in my e-mail, but, according
to the wiki article, the Charleroi plant, which has been putting out
Corning products since it was acquired back in the Thirties. Of
course, whether anyone at Corning’s R&D division had told World
Kitchens that this would be a great idea will probably never be known.
As to the history of labware, I don’t know what was used before the
invention of borosilicate glass by the Germans in the late 1800s. One
alternative might be pure quartz (silica), which has even superior
thermal properties, but is very expensive to produce and tricky to
form. It might be mentioned here that borosilicate glass were not
developed around the needs of the laboratory or the kitchen, but in
lighting, both for those pesky, new-fangled electric-arc street
lights, which get hotter than kerosene or gas-lit lamps, and portable
railroad lanterns, each which are subjected to thermal shock when it
rains.
I suspect that earlier chemists just raised temperature very
carefully, probably using steam heating mantles to prevent
uncontrolled heating, and used metal apparati when sharp thermal
gradients were unavoidable. |
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| Nomen Nescio... |
| Posted: Tue Oct 13, 2009 6:52 am |
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Guest
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[quote:4f0dcf89c4]As to the history of labware, I don~Rt know what was used
before the invention of borosilicate glass by the Germans
in the late 1800s.
[/quote:4f0dcf89c4]
I don't know either, but Lavoisier et al. certainly used
glass bulbs (balloons) of some sort and there are portraits
of alchemists (pre-1700s) with glass retorts, etc.
But chemists also used porcelain, clay, ceramic and metal pots
for cooking their reactions. |
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| Salmon Egg... |
| Posted: Tue Oct 13, 2009 6:35 pm |
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Guest
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In article
<293d2b36-7436-42dd-9742-2fa453f323cd at (no spam) m20g2000vbp.googlegroups.com>,
normfromga <normfromga1 at (no spam) cox.net> wrote:
[quote:b85e2d704d]As to the history of labware, I donąt know what was used before the
invention of borosilicate glass by the Germans in the late 1800s. One
alternative might be pure quartz (silica), which has even superior
thermal properties, but is very expensive to produce and tricky to
form. It might be mentioned here that borosilicate glass were not
developed around the needs of the laboratory or the kitchen, but in
lighting, both for those pesky, new-fangled electric-arc street
lights, which get hotter than kerosene or gas-lit lamps, and portable
railroad lanterns, each which are subjected to thermal shock when it
rains.
I suspect that earlier chemists just raised temperature very
carefully, probably using steam heating mantles to prevent
uncontrolled heating, and used metal apparati when sharp thermal
gradients were unav
[/quote:b85e2d704d]
I also am no expert on the subject. I think I remember reading the
Schott might have developed borosilicate optical glass for Zeiss. Much
of current optical glass is borosilicate. The chemical pyrex is not of
good optical quality. Pyrex microscope slides are an example. I do not
know if that is intrinsic to the formulation or merely a result
manufacturing technique.
Bill
--
Private Profit; Public Poop! Avoid collateral windfall! |
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