> Beginning in the 1980s, production of clear Pyrex glass products manufactured by Corning (and later Instant Brands, after the consumer division was spun off and renamed) was also shifted to tempered soda–lime glass, like their popular opal bakeware.[27] This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly. However, its thermal shock resistance is lower than borosilicate's, leading to potential breakage from heat stress if used contrary to recommendations. ...
> The differences between Pyrex-branded glass products has also led to controversy regarding safety issues—in 2008, the U.S. Consumer Product Safety Commission reported it had received 66 complaints by users reporting that their Pyrex glassware had shattered over the prior ten years yet concluded that Pyrex glass bakeware does not present a safety concern. The consumer affairs magazine Consumer Reports investigated the issue and released test results, in January 2011, confirming that borosilicate glass bakeware was less susceptible to thermal shock breakage than tempered soda lime bakeware.[30] However, they admitted their testing conditions were "contrary to instructions" provided by the manufacturer.[26][31] STATS analyzed the data available and found that the most common way that users were injured by glassware was via mechanical breakage, being hit or dropped, and that "the change to soda lime represents a greater net safety benefit."[28]
1) Pyrex cookware is NOT "likely to crack and split in microwave cooking".
These incidents are RARE.
2) The Pyrex name (in the US) includes both soda lime and borosilicate glass. Warning about "Pyrex" is wrong - you should be warning either about soda lime glass, which include many brands besides Pyrex.
3) Thermal shock is much more likely to occur when moving glass from the freezer to the oven, or from the oven to a metal surface, NOT when cooking in the microwave.
I went ahead and skimmed the video. Every example was of putting a hot pan into a cold liquid, with warnings about moving a hot pan to a cold metal surface, or using it to cook on a stovetop.
There were no examples of shattering due to the microwave turntable, nor warnings thereof.
4) My microwave uses a glass turntable. Why doesn't it shatter? Where does the thermal shock come from between the glass container and the glass turntable?
If the thermal shock is between those two, then surely your more worried the glass would shatter if you take it out of the microwave oven and put it on a metal countertop, yes?
(I bet my glass turntable is made of soda lime glass.)
5) Glass shatters for other reasons, like dropping it. As I quoted, "the change to soda lime represents a greater net safety benefit", because soda glass is safer than borosilicate when that happens.
Don't forget that borosilicate glass also cracks with thermal shock.
"Don't forget that borosilicate glass also cracks with thermal shock".
Hardly. Borosilicate glass has a very low thermal expansion coefficient compared to soda lime glass. Which translates into much lower mechanical stress due to temperature gradients.
This is why laboratory glassware is made from borosilicate glass. Such glassware can safely be held in a flame (kitchen: stovetop use), which is not safe with soda lime glass (tempered or not).
Breakage of soda lime glass may happen due to this difference in material properties.
For example: an oven dish 'burns', what do people do: rush it out of the oven (no problem), place it on a towel (no problem), or dump it in the kitchen sink. In the latter case: oven-temperature glass on ambient temperature metal plate. Bonus points if kitchen sink is wet for improved contact.
This "water splashes in sink" (or on kitchen countertop) causes certain areas of the oven dish to go to near-ambient temperature, while rest of the dish remains at near-oven temperatures. This is what causes difference in thermal expansion -> mechanical stress -> breakage. Small puddles of water in sink or kitchen counter are easy to overlook when someone's in a hurry because smoke comes out the oven. :-)
Hence the advice to place oven dish on DRY surface that conducts heat poorly, like towel, wood, or silicone sheet.
Borosilicate glass is much more likely to survive this type of abuse.
Note this says nothing of mechanical abuse like chip damage / scratches, dropping on the floor, hitting other objects, or some combination thereof. Tempered soda lime glass may well have an advantage there (but any object & its material has its limits of course).
"""We baked at least five samples of each brand in a 450-degree oven. All of the U.S. Pyrex and Anchor dishes shattered when placed on the wet countertop. None of the European dishes made of borosilicate broke, except one practice-run Arcuisine Elegance dish that had been through two baking cycles in our lab. At 400 degrees, we tested two samples each of the U.S. brands against two samples of Arcuisine. All of the American-brand dishes broke but the European brand did not.
When the oven was turned up to 500 degrees, all three of the European Pyrex dishes broke and two of the three Arcuisine dishes broke. We also tested a decades-old Pyrex dish in like-new condition given to us by a staff member's mother. Made by Corning of borosilicate glass, it didn't break, even at 500 degrees"""
The European Pyrex dishes were made of borosilicate glass.
To be very clear, these temperatures are extremely high, and "the test was contrary to instructions on the back of the label." The goal of the test was to see what the safety margin might be for cookware which might get scratched or damaged over time.
> Tempered soda lime glass may well have an advantage there (but any object & its material has its limits of course).
The sources I pointed to say it does have the advantage, and that advantage outweighs the thermal shock advantage.
Pyrex cookware can break in the microwave. So can glass cookware from other brands.
These incidents are RARE.
Your original claim is that they are "likely." This is wrong. Your new claim is that it "breaks in the microwave". Leaving out a qualifier implies it is inevitable and common. That interpretation is clearly wrong given the hundreds of millions if not billions of such glassware in use.
"Pyrex" is a brand name. You need to be specific. Do you mean Pyrex soda lime glass, Pyrex borosilicate glass, or both?
Why do you not care about non-Pyrex brand glassware?
> The platen glass is doped with a microwave absorbance metal to provide some protection to the magnetron
I am not able to verify this claim. As best I can tell, I was wrong - borosilicate glass is most often used, not lime soda. See https://patents.google.com/patent/JP2013063861A/en ("As the glass used for the turntable, borosilicate glass having a low thermal expansion coefficient and excellent thermal shock resistance is used.")
While boron is a metalloid (not a metal), it is not chosen for microwave absorbance reasons.
I do not believe your claim is true because "microwave absorbance metal" means the glass will heat up faster than otherwise, which is not what you want.
Your original text contained this line: "The above is why Pyrex cookware is likely to crack and split in microwave cooking". I've emphasized where you wrote "likely", which you can verify at https://news.ycombinator.com/item?id=36839086 .
> it is hotter than ambient temperature, microwave energy has been absorbed across the large surface area.
Sure. Agreed. That's why I wrote "the glass will heat up faster than otherwise" with emphasis added to show how I know the glass will heat up no matter its composition.
Put your 1.75QT - 1.65L Pyrex cookware in the microwave, by itself, and it will also heat up. That's not a sign that there is some special additive.
You think the glass turntable contains a metal additive which absorbs energy. This means it will get hotter than glass without the additive. Where is your evidence that it is designed this way?
> Beginning in the 1980s, production of clear Pyrex glass products manufactured by Corning (and later Instant Brands, after the consumer division was spun off and renamed) was also shifted to tempered soda–lime glass, like their popular opal bakeware.[27] This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly. However, its thermal shock resistance is lower than borosilicate's, leading to potential breakage from heat stress if used contrary to recommendations. ...
> The differences between Pyrex-branded glass products has also led to controversy regarding safety issues—in 2008, the U.S. Consumer Product Safety Commission reported it had received 66 complaints by users reporting that their Pyrex glassware had shattered over the prior ten years yet concluded that Pyrex glass bakeware does not present a safety concern. The consumer affairs magazine Consumer Reports investigated the issue and released test results, in January 2011, confirming that borosilicate glass bakeware was less susceptible to thermal shock breakage than tempered soda lime bakeware.[30] However, they admitted their testing conditions were "contrary to instructions" provided by the manufacturer.[26][31] STATS analyzed the data available and found that the most common way that users were injured by glassware was via mechanical breakage, being hit or dropped, and that "the change to soda lime represents a greater net safety benefit."[28]