It’s not often that Hackaday brings you something from a cooking channel, but [I Want To Cook] has a fascinating look at Pyrex glassware that’s definitely worth watching. If you know anything about Pyrex it’s probably that it’s the glass you’ll see in laboratories and many pieces of cookware, and its special trick is that it can handle high temperatures. The video takes a look at this, and reveals that not all Pyrex is the same.
Pyrex was a Corning product from the early 20th century, and aside from its many laboratory and industrial applications has been the go-to brand for casserole dishes and much more in the kitchen ever since. It’s a borosilicate glass, which is what gives it the special properties, or at least in some cases it used to be a borosilicate glass. It seems that modern-day American Pyrex for the kitchen is instead a soda glass, which while it still makes a fine pie dish, doesn’t quite have the properties of the original.
The video explains some of the differences, as well as revealing that the American version is branded in lower case as pyrex while the European version is branded uppercase as PYREX and retains the borosilicate formulation. Frustratingly there’s no quick way to definitively tell whether a piece of lower-case pyrex is soda glass or not, because the brand switch happened before the formulation switch.
In all probability in the kitchen it makes little difference which version you own, because most users won’t give it the extreme thermal shock required to break the soda version. But some Hackaday readers do plenty of experiments pushing the limits of their glassware, so it’s as well to know that seeking out an older PYREX dish could be a good move.
If you’d like to know more about glass, we’ve got you covered.
I’m surprised by this, because as far as I know it should usually be very obvious simply by inspection.
Soda-lime glass has an green tint which is visible when looking at an edge or other thicker area (while it’s possible to tint the glass to compensate, it doesn’t look like pyrex bothers.) Borosilicate glass has either a bluish or no tint. Every piece of pyrex shown in the video exhibits this characteristic.
it i even obvious in he thumbnail
The bluish/greenish tint unfortunately isn’t a completely reliable test, since it’s caused by iron contamination and can appear in either kind of glass. A more reliable test is to submerge a piece in glycerine. Borosilicate has the same refractive index and will look invisible; soda-lime glass won’t.
A good thread on distinguishing them is here: https://www.sciencemadness.org/whisper/viewthread.php?tid=158521
I looked this up, and there is a great demo here: https://www.reddit.com/r/chemistry/comments/kdom18/fun_fact_glycerin_has_the_same_refractive_index/
When it’s a jar?
All of that glassware has an entirely open top, it’s a bit more than a jar.
Someone tried to tell me a door was a jar the other day, I told them they must be rather stupid, I can plainly see it’s a door and not a jar.
Good to know that after 27 years of switching to soda-lime glass someone made a Youtube video explaining these differences.
how does PYREX compares to german SuperFest ?
Superfest is, as far as I know, soda-lime glass with a surface treatment, so not suitable for high temperature use.
completely different, superfest is more like gorilla glass
SuperFest and “pyrex” are both strengthened glass. SuperFest is chemically strengthened (similar to Gorilla Glass) and “pyrex” is tempered. Both processes generate significant compressive stress in the outer layers of the glass which need to be overcome in order to break it, making it more impact resistant.
“PYREX” gets it’s temperature resistance primarily it’s low thermal expansion coefficient. So heating it doesn’t generate the same stresses in it as in soda-lime glass. But since it doesn’t go through a secondary strengthening process, it’s impact resistance is lower.
My favorite sighting of off-brand Pyrex glassware was branded “Fire King”. That always made me smile. (Think Latin)
Simply pulling empty glassware out of the oven is often enough to crack it.. with nothing in it it cools rather quickly.. and this wouldn’t be impact resistance.. just low thermal expansion coefficient.. what about lab glassware.. surely it still needs the properties of original Pyrex ?
Explains why my “pyrex” dish exploded into a million little pieces all over the kitchen when it was taken out of the oven and put on the stove glass cooktop.
Frustratingly there’s no quick way to definitively tell whether a piece of lower-case pyrex is soda glass or not
I mean there is one way and it sucks. It is destructive testing. Take it out of the oven or off the open flame cooktop and put in an ice water bath. If it shatters … you didn’t want that anyway. If it does not break it’s either legit borosilicate or it will suit your purposes fine anyway.
.
When I heard of the switch I committed to just buying used from thrift shops, garage sales etc.
.
Proper labware like beakers and stuff still works fine for kitchen use anyway plus has a groovy mad-scientisty vibe as well. And are pretty inexpensive.
… and for a groovy mad-scientist-mathmatician vibe, there’s ACME Klein bottles- Accept no substitutes!
I’m pretty sure the article get’s the PYREX vs. pyrex, American vs Euro story wrong.
IIRC
Corning screwed up it’s US trademarks and only got ‘PYREX’, not lower case ‘pyrex’.
How that’s not ‘confusingly similar’ is beyond me, but not a lawyer.
Could just have been a courthouse spending contest, that’s how those things work IRL.
You can still get Borosilicate ‘PYREX’ branded, from Corning, in the USA.
You can also get ‘pyrex’, for much less money.
It’s always soda glass, except when it’s just plane glass.
You can guess what’s on the shelf at wallyworld.
The crappiest chinesium available, same as always.
You can’t get PYREX cookware from Corning anymore, only PYREX labware.
“pyrex” banded cookware comes from Corelle Brands, formerly World Kitchen, formerly Corning Consumer Products Company, a division of Corning. They were spun off from Corning in 1998, but the creation of the “pyrex” brand and the use of soda glass for some “pyrex”-brand consumer cookware happened while they were still a division of Corning. Corelle did switch to soda glass for all products after the spin-off and claims that 95% of its pyrex cookware are made in the US.
Currently, Corning only sells industrial PYREX borosilicate products in the US. Elsewhere, I believe partners and not Corning sells borosilicate cookware with the PYREX branding.
there are a lot of people trading on the name, but not doing the original glass.
ie https://www.pyrex.eu/en-eu/pages/a-unique-glass
Note it their description ” *Thermal and mechanical resistance compared to competing products made of borosilicate glass.”
As best as I can tell, legitimate Pyrex has its trademarked name typed in blocky letters and surrounded by that oblong. The other tell is that it always carries metric units (at least in Europe).
My advice? Buy the IKEA ones. They specify the glass composition on the website.