Facts about Pyrex

Some of you may have heard that newer pyrex is not as good as the old stuff. The following may interest you:

Pyrex was invented ca. 1915, the brand owned by Corning.

First, note that there are two types of glass in question. Ordinary glass like in windowpanes or drinking glasses, which are made from soda-lime, and the more expensive borosilicate glass that is used in the original pyrex. (Before any objections are raised, there are many other types of glass.)

Along the way, Corning owned Corelle, which manufactured pyrex, and Corning also had a licensing agreement with Newell Cookware Europe. In 1998 Corning and Corelle split. After that Corelle switched from borosilicate to the lower-quality soda-lime to make their pyrex. Newell never changed the formula and their European cookware is still borosilicate.

So how can you tell which you have? Is the glassware you're inspecting at a garage or estate sale the real stuff or the inferior stuff? Easy. There several ways to determine which is which, but two methods are extremely simple.

First, look at the edges. Everyone has probably seen the edge of a sheet of glass. It's green and pyrex made of soda-lime glass is also green on its edges. The borosilicate type is colorless.

Second, (this is too easy) look at the logo on the glassware. If it says PYREX, it's borosilicate; if it says pyrex, it's the cheaper soda-lime.

So now go check your measuring cups, pie pans, and loaf pans.

Mine all say PYREX; no surprise, they're all old. I even have a couple Corelle dinner plates!

Mine all say PYREX; no surprise, they're all old. I even have a couple Corelle dinner plates!

I have a mix: a couple of lowercase pyrex loaf pans; everything else is uppercase. I have a stack of Corelle plates that we ordinarily eat off. Not sure where we got them.

[Jenise]

Interesting, Larry, didn't know. My measuring cups are pyrex at best. I mean, they're brand Pyrex, but I replaced my four cup many years ago and the new 4 cup irritates because the pouring spout is much shallower than the old one was. Too shallow for thick stuff like batters--stuff overflows if you pour any faster than 1 tblsp per minute, or what feels like that.

We bought second hand Corelle for our travel van. They're so thin and they stack so tightly--meaning the fit in a small vertical space and don't shift/clank--we keep six Corelle plates upright on their side and, made out of unbreakable plastic suitable for having on boats, six more plates, six juice glasses, six bigger glasses and four cereal bowls all of which nest well in one plastic bin about the height of the plates and just 5 inches wide. For space efficiency in a place where every inch is a premium, doesn't get any better than that.

I am a container nut! Especially anything for the kitchen -- and PYREX glassware. I knew there was a difference, but I never knew exactly how or why. For me, it's about anything with a minor lip on the edge. If it has a straight edge, I'm usually not interested, unless it is glass bakeware. Now you are going to have me pull out everything I own and look for the "union label". GRRRRR! But, I'm also feeling a little like having some terrible disease I'd really rather not know about. GRRRR!!! On my way to the kitchen.

[Robin Garr]

I never knew any of this either! Naturally I had to go look, and sure enough, the two-cup measure that I use all the time is a lowercase pyrex, with the telltale green edge.

But here's a workaround! I never noticed this, just assumed it was Pyrex brand, but my one-cup measure isn't labeled Pyrex, it's labeled ... Oven Basics! It has an Anchor Hocking anchor logo discreetly etched into the bottom, and it does not flash green. Who knew!?

Oven-Basics.JPG

Borosilicate glass tolerates higher temperatures better than soda glass because it expands less when heated. Because of this thermal expansion property it is the glass of choice for amateur telescope mirrors. When Corelle switched to soda glass, there was a minor crisis in the amateur Astronomy world as PYREX mirrors disappeared from the market. Fortunately other manufacturers have stepped up to provide annealed borosilicate glass to the amateur Astronomy market.

-Paul W.

Right on.

There was a time in my younger days when I thought I would grind my own pyrex telescope mirror and even bought some grinding powder. But, like many things, I never got around to it.

But here's a workaround! I never noticed this, just assumed it was Pyrex brand, but my one-cup measure isn't labeled Pyrex, it's labeled ... Oven Basics! It has an Anchor Hocking anchor logo discreetly etched into the bottom, and it does not flash green. Who knew!?

Yes, I have some medium-size glass cups that are absolutely heat-resistant and I always thought they were PYREX but now I see they are actually a Turkish manufacture, Paşabahçe.

[David M. Bueker]

I just have some high temperature lab equipment. Works great.

I'd add that there are other brands that also make borosilicate glass. I have a 1 l. Bomex Florence flask that I use as a 'Hoggit' decanter. I had a friend tub me up a wooden base that it sits in. Fill with wine and pass around the table and they can't set it down, it has to come back to the starting point - no one can 'hoggit'. Used to be a way of not having to always say "Pass the Port, you bounder!"