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Pyrex and Anchor Hocking now both unsafe for cooking

I’m not sure how I happened upon Consumer Reports’ disturbing feature from January on exploding glassware cooking accidents in both Pyrex and Anchor Hocking tempered glassware. Since a lot of my microwave directions call for Pyrex bowls, I thought I’d better post about it asap.

Here’s the link explicitly:


Because I’ve used my current Pyrex bowls and bakeware for more than 10 years, I’ve been looking recently to replace and/or add to my collection. But every time I’ve looked for it in the past year or so, I’ve hesitated–the stuff on sale is a blueish color. Or it’s a little thinner than I remember. Or it doesn’t feel or even sound right when I pick it up. And the cardboard overwrap has a lot of new warnings about when and how you can or can’t use it that are different than the old classic Pyrex. It’s confusing–can I use it the way I’m used to or not?

So even though the casseroles and pie plates are bright and shiny and new and usually on sale at my local supermarket and the Target, I’ve passed them up, thinking, “I’ll do it next time.”

According to the Consumer Reports piece, it’s a damn good thing I did. Read the article. Now. Please. Before you put any of this generation of Pyrex in an oven or microwave. Before you give a set to some newlywed as a kitchen gift.

And don’t buy this stuff. If you did, don’t use it for any kind of heating up, conventional oven or microwave (I know, so what good is it if you can’t heat stuff up in it? Wasn’t that the whole point?)

Apparently both companies are claiming that the explosions–which have caused burns and lacerations when the victims took a hot casserole out of the oven or microwave and set it down–are the result of misuse, or perhaps the glassware had gotten dinged or scratched and therefore the flaws had weakened it, and that it was a rare phenomenon. The article authors estimated a fairly high number of incidents in the past few years based on hospitalization records and other outside evidence.

Consumer Reports debunked the companies’ blame-the-victims ploy by testing both brands of glass cookware at various temperatures and setting the pans down on a variety of typical kitchen surfaces.

The results were not pretty–Pyrex had a slight temperature range advantage over Anchor Hocking, but a fairly high percentage of both broke or exploded if they weren’t used exactly within the laundry list of restrictions on the cardboard overwrap that came with the new bakeware.

Altogether, conducting the tests and videorecording them took more guts than I would have without lexan armor and a full face shield.

But, as I’ve said, I’ve been using my mixing bowls and pie plates for years without problems. What’s going on?

The article authors did track down a probable explanation for all this breakage in what’s supposed to be very durable glassware. Both brands have recently switched to a cheaper formulation for their glass. Pyrex–note, no longer made by Corning–at least used to be borosilicate glass but now uses soda lime glass, as does Anchor Hocking’s tempered glass. Borosilicate is the standard for laboratory grade glassware; it’s stronger and somewhat more expensive to produce–probably the mineral shortages of the past few years have made it more so.

Technically, you can temper soda lime glass, but even when tempered it’s not as strong as the old classic tempered borosilicate. It also seems to be less uniform–and the little unevennesses in the material create local instabilities that can cause cracks and even explosions when subjected to rapid or uneven heating and cooling. It only takes a split second in some cases.

Borosilicate is almost certainly what my old Pyrex standbys are made of, and I’m standing by them. I just wish I could have bought more at the time, or that someone else made them now. I wish Pyrex’s current manufacturers in particular had not ruined their product by changing glass to reduce costs, and that their managers weren’t scrambling to deny it.

For now, I’d say please DON’T use the newer Pyrex or tempered glass bakeware items for microwaving. They’re just not the same anymore. Use microwave-safe ceramic instead.

4 Responses

  1. Thank goodness mine is all old stuff. I agree, what good is it if you can’t heat it? I suggest haunting garage sales. I got a couple old Pyrex pie plates for $1 each from someone who was selling off all Mom’s stuff from the 70’s.

    • Wish I could–but I keep kosher, and pyrex is considered slightly porous so I can’t go with someone else’s used stuff. The usual boiling to kasher it (as with silverware or regular glass) isn’t allowed for wood, plastic, or pyrex. Though I wonder why anyone would give up their old pyrex if it’s still useable.

      • I couldn’t believe it either. I was all “Really?” Got a bread machine for $5 and the pie plates. It was late in the day and they had an “everything must go” mentality.

        I wonder why Pyrex is considered porous? Back in my chem lab days, it was regarded quite the opposite. I’ve got a few pieces of labware left and I’m sure that’s safe to heat, after putting it directly in Bunsen burners.

      • The rules of kashrut are about eating or not eating certain foods for religious purposes–so symbolism takes priority over purely physical considerations, and it doesn’t always make a great deal of sense to the outside world. The rabbinical committees that investigate new materials or ingredients to see what category to put them in do the best they can with the science–sometimes the modern world gets ahead of them, and with all the upgrades available (just as for computers) standards start to shift. If something’s porous, the idea is that food will catch in the pores, and you can’t get it all out to make the item perfectly clean, even by boiling. Pyrex is more porous than untempered glass, according to what I was taught, but of course it’s not actually very porous. For example, I’d say pyrex is a lot less porous than limestone, which was considered impervious and nonporous and therefore kasherable way back in the temple days. When it was smoothed and polished, it had a lot fewer visible holes than most of the ceramics of those times. There’s at least one such carved limestone cup from about 2000 years ago in the Israel Museum in Jerusalem. Still in pretty good shape, actually, even after my daughter stood there reading the ENTIRE caption (page-long) for 15 minutes out loud. If it could survive that, I give it another 2000 years, easy.

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