Some Questions About Pyrex and Corningware

[Chris Hennes]

Thank you for that link.  After reading the reports of injuries I quickly questioned what abuse had taken place but had no way of suggesting an authority that would back up my sense that Pyrex when properly used is very safe.

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It is important to note that Pyrex can shatter, it is simply more resistant to it than other ceramics. If it gets scratched or damaged in any way, throw it out. It cannot deal with high gradients in temperature, so you should always preheat your oven, etc. I see no credible evidence that it spontaneously explodes absent these causes, however. Checking ConsumerReports.org gives no hits, and I would expect them to be on the problem like rabid dogs if there were a real issue. I think the stat is something like over 100 million pieces of Pyrex are manufactured every year.

[JMT]

I have used a Bunsen burner to dry labbglass made out of pyrex on several occasions, never had any problem. The labbglass tends to be much thinner but generally it should be safe. The only time I wouldn't do it would be if I saw some sort of crack in the middle of the glass.

[K8memphis]

I have used a Bunsen burner to dry labbglass made out of pyrex on several occasions, never had any problem. The labbglass tends to be much thinner but generally it should be safe. The only time I wouldn't do it would be if I saw some sort of crack in the middle of the glass.

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I think the cracks and weaknesses are easy to overlook.

If it breaks on yah I think you can be assured there was one.

[jsmeeker]

custards are baking in the oven right now. I'll find out how this goes later tonight.

[dougal]

It is important to note that Pyrex can shatter, it is simply more resistant to it than other ceramics. If it gets scratched or damaged in any way, throw it out. It cannot deal with high gradients in temperature, ...  I see no credible evidence that it spontaneously explodes absent these causes, however. ...

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Yes indeed.

When Pyrex does break, it tends to go quite dramatically.

It isn't bulletproof.

Scratches act as "stress concentrators" potentially multiplying many-fold any stresses on (and in) the piece.

If you can see scratches - bin it. You don't want to see what can happen.

Don't put cold stuff into a hot Pyrex dish.

And the other way round, don't set a hot dish on a cold or wet surface! (My guess as to the cause of many of these problems.) Set it on a wooden board, or somesuch.

But, hey, it should be absolutely ideal for using a flame to finish a creme brulée... really.

[DerekW]

Interesting. We have a number of Pyrex [and similar] glass items in use in the kitchen. Useful equipment.

I have an approximately two inch long scar arcing along the side of my hand and up onto my small finger, imparted by a flying fragment of a Pyrex jug which exploded in my hand a couple of years ago. The jug bore no noticeable scratches at the time, was not being and had not been previously mistreated. Numerous stitches and messy blood loss were involved. This didn't happen to my sister's friend's aunty Jean, it happened to me. Stuff happens.

Glass, even competently tempered, can retain internal stress sometimes sufficient to cause breakage from causes so vanishingly small as to appear spontaneous, even years after manufacture. This was explained to me by the manager of a reputable art-glass manufacturer, whose team were at that time crafting a replacement for a piece which had cloven itself after a decade or so of sitting peacefully on a shelf.

I'd torch the brulee with care but not much concern.

[jsmeeker]

It worked. No exploding glass. Creme Brulee was tasty, too.

[Chris Hennes]

It worked.  No exploding glass.  Creme Brulee was tasty, too.

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Good the hear---I'd have felt really bad if you hurt yourself!

[Wholemeal Crank]

On KCRW's Good Food podcast for 8/22/09, a guest was discussing pies with the Evan Kleinman, and mentioned an episode of 'exploding pie' because her pyrex pie plate 'lost its temper' and exploded. She said pyrex expires!

I've never heard of this phenomenon. Anyone know what she is referring to?

[Chris Amirault]

Interesting! Over on the USG's "Ask a Scientist" website, we have this exchange:

Would you please tell me why a Pyrex casserole that I have used for years would explode when I took it out of the oven. It was hot but I placed it on the top of the stove to cool. It exploded into very small shards of glass.

* * * * *

Several things may have happened.

1. One tip-off is your comment "I have used for years...". Glass (Pyrex) and others can develop invisible (except using a pair of polarizing filters) stresses that finally cause the bowl to crack. Once a crack starts to propagate it can shatter into small shards.

2. If you had scratched or chipped the bowl ( and it could have been small enough that you might not even be aware of it) this too sets up stress sites that allow (1.) to occur more readily.

That doesn't sound like milk going bad; that sounds like materials science: little stress points build without your awareness and the whole sheebang loses integrity.

Has this happened to anyone? And why is poor Pyrex being blamed? Does it happen with Corningware too?

Edited September 16, 2009 by Chris Amirault
clarify quotation (log)

[Kouign Aman]

This answers part of the Q on another discussion about why glass refrigerator dishes went out of style!

[HungryC]

Never had a Pyrex dish shatter--borosilicate glass is way harder to scratch than plain ol' glass. I have seen the nasty results of Corningware's delamination---a bazillion needle-sharp shards. I used a Corningware bowl to feed my outdoor cat, and his enthusiastic eating moved the bowl quite a bit on the rough, concrete patio. One day, I dumped in the kibble, and kapow--it just shredded. Scared the hell out of me & kitty. He wouldn't eat out of a bowl at all for a few days!

[lemniscate]

If you do a google search of "pyrex explodes" or "pyrex exploding" there's lots of hits. A theory is that the newer Pyrex is not made out of borosilicate glass anymore. I have had a newer Pyrex rectangular dish crack in half in the oven (it was a very new dish) but not reduced into shards. The old 60's/70's pyrex and fire king I inherited have never chipped, cracked or shattered in almost daily use. Just my gut, but I don't trust the new glassware now. I have never heard of expiring glassware before.

[baroness]

Glass is one of my passions and a favorite creative medium. I may know more about glass than food!

Glass cannot expire or 'lose its temper'.

There are things that can stress the glass, thus opening the door to problems:

IN MAKING THE ITEM

Incompatible glasses mixed in the making of the item

Bad technique when joining parts

Improper annealing during the making of the item

ITEM IN USE

Sudden, dramatic changes in temperature (freezer to oven or broiler; oven or stovetop to a cooler surface, particularly if it is wet as well)

Surface scratching (if you have ever cut glass, this is obvious!)

Borosilicate glass is more resistant to breakage than softer glass. I have heard that at least some Pyrex is now foreign-made. Some of the Asian boro that is used for ART GLASS is pretty bad quality (and cheaper, of course) than American boro.

Some of my newer (foreign-made) Corningware prohibits stovetop use, a change from the American products.

I do not fear baking in glass, but do treat it with reasonable care.

[thock]

Actually, it can lose its temper, as in become untempered, if it's tempered glass. The newer Pyrex is now made out of tempered glass, not borosilicate glass, at least in the USA. In Europe, you can still get borosilicate Pyrex.

Tracy

[baroness]

From the pyrexware.com website: "PYREX® glass products are made using a tempered soda lime glass composite, as is the vast majority of consumer glass bakeware in the North American marketplace. The Cookware Manufacturers Association considers soda lime an appropriate material for glass bakeware."

Soda-Lime glass, whether 'tempered' or not, has no place in MY kitchen. It is heavier, weaker, and far more temperature sensitive than borosilicate. I'm grateful that I don't need any new pyrex-type items!

[Wholemeal Crank]

This is all so interesting to know!

I will continue to treasure my older pyrex, and be glad that I got a lot of my casseroles through thrift shops rather than new.

[MSRadell]

From the pyrexware.com website: "PYREX® glass products are made using a tempered soda lime glass composite, as is the vast majority of consumer glass bakeware in the North American marketplace. The Cookware Manufacturers Association considers soda lime an appropriate material for glass bakeware."

Imagine that, the Manufacturers Association says that a process can be used to make a consumer product! I wonder what the consumer product safety commission or some of the other consumer organizations think about this? It is certainly not as good as the original product, only cheaper.

[andiesenji]

I too have many pieces of Pyrex, FireKing, Glasbake and other glass baking dishes as well as some stovetop glass pieces that have survived since the 1930s without breaking.

I never subject them to abrupt temperature changes because I know that is specifically forbidden.

The instructions that came with the original glass cooking vessels specified placing the hot dishes on a folded DRY towel. Good advice today.

If the casserole was removed from a hot oven and placed on the stovetop, I assume it was placed on the burner grid. That metal works as a heat sink (unless it has been pre-heated) and the effect can be sudden destruction of the piece.

When the newer and thinner borosilicate glass containers first appeared on the market in the 1970s, they were sold with cork pads and the instructions were specific that they should be placed on the cork when removed from the heat - especially should not be placed on a ceramic tile surface (another heat sink) and the same goes for granite, etc., etc.

I don't care about all the technical jargon, I simply use common sense. Glass, ceramic and their relatives simply do not have the capacity to survive sudden temperature changes.

[Lisa Shock]

I broke an item this summer and replaced it, and now, I notice that the top edge has a green color, whereas my older items have a clear edge. Hope this helps!

[John Rosevear]

Does anyone know of a current-production brand of decent borosilicate kitchen glass? Clearly Pyrex is No Longer The Thing, at least in the US. Has anyone else stepped in? Alternatively, if the Euro Pyrex is still the good stuff, can anyone recommend a source that will ship to a US address for non-crazy money?

[thock]

Target has sold some borosilicate baking utensils from Green Apple, with a non-stick coating that is translucent. The coating is proprietary. I don't know whether Target still carries it, but I think you could search for it online.

[thock]

I too have many pieces of Pyrex, FireKing, Glasbake and other glass baking dishes as well as some stovetop glass pieces that have survived since the 1930s without breaking.

I never subject them to abrupt temperature changes because I know that is specifically forbidden.

The instructions that came with the original glass cooking vessels specified placing the hot dishes on a folded DRY towel. Good advice today.

If the casserole was removed from a hot oven and placed on the stovetop, I assume it was placed on the burner grid. That metal works as a heat sink (unless it has been pre-heated) and the effect can be sudden destruction of the piece.

When the newer and thinner borosilicate glass containers first appeared on the market in the 1970s, they were sold with cork pads and the instructions were specific that they should be placed on the cork when removed from the heat - especially should not be placed on a ceramic tile surface (another heat sink) and the same goes for granite, etc., etc.

I don't care about all the technical jargon, I simply use common sense. Glass, ceramic and their relatives simply do not have the capacity to survive sudden temperature changes.

Andie,

Do you put your borosilicate glassware in a pre-heated oven? I haven't been, because I'm concerned that it will crack. However, I do remember my mother putting Corningware and Pyrex in a pre-heated oven.

[baroness]

I'm not Andie, but I use my Pyrex and the like in a pre-heated oven. How else could one bake?

[prasantrin]

Pyrex can go from cold to hot--it can even go from freezer to a hot oven. It just can't go the other way around.

Other info from the Pyrex website (bolding is mine):

First, and most important, we want to assure all PYREX consumers that PYREX glass bakeware is and always has been safe to use when our Safety & Usage Instructions are followed. PYREX glass products are used in about 80 percent of U.S. homes and have maintained an excellent safety record for generations. Importantly, the Consumer Product Safety Commission, the federal agency charged with ensuring the safety of consumer products, has reviewed PYREX glass bakeware products and found no safety issue. There has never been a recall of PYREX glass bakeware.

It has been wrongly reported that World Kitchen is not a U.S. company, and that PYREX glass bakeware is now made in China. This is not true. PYREX glass products have been made in the U.S. since 1915. We continue to manufacture PYREX glass products in our Charleroi, Pennsylvania plant with union labor and our packaging displays the American flag and the "made in the USA" label.

It has also been wrongly suggested that World Kitchen lowered the quality of PYREX glass bakeware by switching from borosilicate glass to soda lime glass. Again, this is not true. The Charleroi plant has produced PYREX glass products out of a heat-strengthened (tempered) soda lime glass for about 60 years, first by our predecessor Corning Incorporated, and since 1998 by World Kitchen. In fact, since the 1980's, most, if not all consumer glass bakeware manufactured in the U.S. for consumers has been made of soda lime glass.

And their safety and usage instructions:

NEVER use on top of the stove, under a broiler, in a toaster oven, or place over oven vent or pilot light.

AVOID severe hot to cold temperature changes, including:

DO NOT add liquid to hot dish

DO NOT place hot dish or glass cover in sink

DO NOT immerse hot dish in water

DO NOT place hot dish on cold or wet surfaces

Handle hot ovenware and glass covers with dry potholders

ALWAYS add a small amount of liquid to the vessel prior to baking foods that release liquids while cooking.

DO NOT overheat oil or butter in microwave. Use minimum amount of cooking time.

DO NOT use or repair any item that is chipped, cracked or scratched.

CARE INSTRUCTIONS:

To loosen baked-on-food, allow glass to cool, then soak.

If scouring is necessary, use only plastic or nylon cleaning pads with nonabrasive cleansers.

Sometimes it pays to read manufacturers' instructions, even if they are "stoopid".

Edited November 14, 2009 by prasantrin (log)