Do you know there are two logos for Pyrex and do you know what the difference is between them? PYREX or pyrex, which is safer and what’s in your kitchen?
There are three different types of glassware typically found in kitchens? They are soda-lime, tempered and borosilicate.
Borosilicate glass includes boron trioxide, which has a low thermal expansion. Unlike normal glass, it won’t break when exposed to major temperature shifts such as taking a dish from a fridge to an oven. This is thanks to boron trioxide, the element that makes glass resistant to major temperature changes. Pyrex is a sub-group of borosilicate.
Soda-lime glass is the most common glass type in kitchens since it’s used for most drinkware from juice cups to jars. Untreated soda-lime glass is more susceptible to breaking from extreme temperature changes. This shock expands the glass at different rates, resulting in cracks and fissures.
Tempered glass is just soda-lime glass that’s been heat-treated to make it more durable. During that heat-tempering process, the exterior of the glass is force-cooled so that it solidifies quickly, leaving the center to cool more slowly. As the inside cools, it pulls at the stiff, compressed outer layer, which puts the center of the glass in tension.
Are “PYREX” and “pyrex” the Same?
Both trademarks were historically used interchangeably in the marketing of kitchenware products made up of both borosilicate and soda-lime glass.
However, now Corning has licensed out the use of their PYREX (upper case lettering) and pyrex (lower case lettering) logos to other companies.
Lowercase pyrex is now mostly used for kitchenware sold in the United States, South America, and Asia. In Europe, Africa, and the Middle East, uppercase PYREX is still available.
Pyrex used to be made of the more heat-resistant borosilicate glass, which is more resistant to breakage when subjected to extreme shifts in temperature.
Pyrex eventually switched to tempered glass most likely because boron is toxic and expensive to dispose of. Although tempered glass can better withstand thermal shock than regular soda-lime glass can, it’s not as resilient as borosilicate.
If the logo is in upper case lettering, PYREX, it’s most likely made of borosilicate, and thus safer. The lowercase lettering is most likely made of soda-lime glass, so take extra care after any high-heat cooking. Most glassware products will include warnings so make sure to read about proper handling, cleaning, and storage.
All of my measuring cups are pyrex, like my picture above. I have boiled water in them in the microwave with no problem except once when the bottom broke right off, I am proof lowercase pyrex do break. If you ever had a casserole dish prepared ahead of time (you have it in the refrigerator) and the recipe states to take it out for 15 minutes before baking, make sure you do or the extreme cold to hot can shatter that dish as well. Losing the dish is bad but ruining your dinner is not acceptable!
SOURCE: http://www.AllRecipes.com