Pyrex products were made of borosilicate glass until the 1950s. At that point, they switched to manufacturing products with tempered soda lime instead. Today, every piece of bakeware made in the U.S. uses tempered soda lime, including the full line of Pyrex consumer glassware.
Until around the 1950's, all Pyrex products were made of borosilicate glass, which is resistant to thermal shock, a rapid temperature change that can cause something to explode. Corning started producing tempered soda-lime glass at some point in the 1950's but it's not clear when they started the transition.
I contacted Pyrex to ask if there's an easy way to tell what material your Pyrex dish is made from, and the company had a simple answer: Look at the logo. If it's all caps “PYREX,” it's vintage, made of borosilicate. If it's lower case “pyrex,” it's new, and it's soda lime.
The best way is to look at the bottom of the product. My vintage Pyrex, which is at least 40 years old, and definitely boro-silicate, reads “Not For Lab Or Stovetop Use - Corning N.Y. - U.S.A. - 516 - PYREX.” Newer products made of soda-lime glass do not read Corning N.Y., nor are they made by Corning.
“Borosilicate glass is also lead and BPA-free, making it perfectly safe for use as drinking glasses. True borosilicate glass is actually safer than tempered soda-lime glass, which is what many companies currently use to make kitchenware.”
Borosilicate glass is more expensive to produce than ordinary glass due to the inclusion of boron trioxide, which adds to its thermal and chemical resistance. This increased production cost is often passed on to consumers, making borosilicate glass products more expensive.
High thermal resistance: Borosilicate glass can withstand temperature changes without cracking, making it perfect for boiling water. Chemical stability: It is resistant to chemical corrosion, ensuring that it does not leach chemicals into the water when heated.
Baking glassware such as Pyrex dishes in usable condition should be donated to local thrift stores or otherwise reused. If unusable they should be thrown away in the trash. They should not be added to curbside recycling. They are made of a different material than glass bottles and jars.
Patterned Pyrex—such as the 1956 Pink Daisy or the 1983 Colonial Mist colorways—tend to be valuable as a collector's item. Other popular patterns include the 1957 Butterprint, which features an Amish couple and their crops, and has been valued at a few hundred dollars.
Borosilicate glass is sold under various trade names, including Borosil, Duran, Pyrex, Glassco, Supertek, Suprax, Simax, Bellco, Marinex (Brazil), BSA 60, BSC 51 (by NIPRO), Heatex, Endural, Schott, Refmex, Kimax, Gemstone Well, United Scientific, and MG (India).
It could be counterfeit glass! Soda lime and Borosilicate glass look very similar, but perform completely differently. Lately, there has been a rash of counterfeit glass introduced into the glass-gauge industry, some so-called companies even illegally using the corporate names of legitimate glass providers.
This difference means that Borosilicate glass does not expand as much on heating, so it is less likely to break when heated. Pyrex is one particular blend of Borosilicate glass, with a particularly high heating tolerance.
Corning used borosilicate to produce all Pyrex products. However, the company that purchased the cookware products switched to soda-lime glass, adopting the name pyrex (spelled with all lowercase letters).
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.
So, why did Pyrex make the change all those years ago? Two primary causes: increased air pollution regulations and a focus on reducing energy consumption. Soda lime glass is better for the environment, requires less energy to produce, and is more easily recyclable—making it the preferable choice.
It is stronger than regular glass but it can still break or crack if it is dropped or hit hard. It is important to handle borosilicate glass with proper care to minimize the risk of breakage.
A highly-coveted pattern, the Atomic Eyes Chip and Dip is the holy grail for some Pyrex collectors. Released in the 1950s, some of the bowls feature a Pyrex stamp while others don't.
What Makes Pyrex Special. "Pyrex continues to hold its value because most of us associate it with memories of family and holiday gatherings and memories from their childhood," Wright says. "The vintage designs and patterns of Pyrex evoke a nostalgia, which adds to its value for collectors.
The name Cinderella was applied to quite a few different Pyrex products from carafes to butter dishes but the spout and handle nesting bowls marked the first use of this name.
in early 2022, sales of Pyroceram-based CorningWare were temporarily discontinued in the USA but reappeared on the market in early 2023. It continues to be sold in other regions of the world.
Borosilicate glass is the ultimate non-toxic choice. It's completely free from harmful chemicals like BPA, lead, or phthalates. No matter how hot or acidic your food gets, this glass stays clean and safe, giving you one less thing to worry about.
Can Borosilicate Glass Be Recycled? The short answer is yes, but there are some factors to consider when it comes to the eco-friendliness of borosilicate glass. Like any other glass, borosilicate can be remelted repeatedly to make other borosilicate products.
Borosilicate glass is known for its durability, heat resistance, and clarity. It is a type of glass that contains boron trioxide, which gives it unique properties that make it suitable for a variety of applications, including coffee carafes.
What material is safe? You will want to stay away from metallic and porcelain teaware if you want to prevent toxins from leaching into your tea. And the best material for your teapot is something called borosilicate glass. Borosilicate glass is lead and cadmium-free, and it won't leach harmful chemicals into your tea.