"Magic Bowl" effect with an aluminum foil roasting pan

I seem to recall reading something about the nature of pyrex and shattering. I've had an occasional pyrex shatter in my lifetime and well calling it a shatter didn't do justice to the incredible mess and number of fragments.

At any rater, pyrex is more prone to shattering, I think, when it is cooling down. So, if that is the case, where you put the bowl after it comes out of the oven is probably pretty important.

I noticed that there are some very expensive oblong glass roasters on eBay, just incase anyone is interested.

--Pamela

I found the article I read about pyrex on Cook's Illustrated. --Pamela

Published November 1, 1998.

 

When do I risk having a baking dish explode? Can I put a frozen glass pie plate directly from the freezer into the oven?

The problem of exploding glassware is not unfamiliar to us. An editor here had a Pyrex dish containing roux (a mixture of fat and flour) shatter on him after removing it hot from a microwave to a cool, damp countertop. To find out what might have happened in your case and his, we contacted Don Miller, an engineer who supervises the glass lab at the University of California at Santa Cruz.

IMiller offered several possible explanations for our exploding glass. One is that the glass may have been scratched, which, he said, "can happen by many means over years of use. Once this happens, it changes the whole structure of the glass and makes it more vulnerable to breakage." Another is temperature change. "The fact that it broke in many pieces," he said, "leads me to think there was a reaction with . . . a cold surface." Yet another possibility is moisture. If it comes into contact with moisture of any kind, this alone could make the hot glass break. Combine any two or all three of these factors, and you have a recipe for disaster.

We checked out these theories with Jim Kamandulis, senior quality analyst for World Kitchen, the company that owns Pyrex. He concurred on all counts, even giving us a name for such events: down-shock. 

Down-shock occurs when there is a sudden cooling of a glass surface. If any flaws, such as scratches, are present when such rapid cooling occurs, the dish can shatter. The opposite, up-shock (breakage upon a sudden heating of the glass) can also occur, he said, but glass is much more vulnerable to down-shock. 

How to prevent down-shock? Miller suggested inspecting the dish before use by turning the bottom toward your face and then looking into bright light, but often it's impossible to detect a tiny but fatal flaw. It is possible, however, to avoid the problem of contact with a hard, cold, and/or wet surface by placing the hot dish on a clean, dry dish towel. Kamandulis also advises strongly against using even slightly damp potholders to remove a hot Pyrex dish from the oven; they, too, can cause the dish to break, right in your hands. 

Moving Pyrex From the Freezer to the Oven It should be fine to transfer a filled Pyrex pie plate from the freezer into a preheated 425-degree oven. However, Kamandulis emphasized the need to preheat the oven before putting the pie plate in. He explained that the pie plate would likely break if it came into contact with any direct heat source and also that some ovens may use the broiler as well as the bottom heating element to quickly heat up to the desired temperature, resulting in a heat intense enough to be regarded by Corning as the equivalent of direct heat.

The transfer from freezer to preheated oven is okay because the glass from which Pyrex products are made is tempered. Tempering, Kamandulis pointed out, is a mechanical strengthening process that increases the thermal shock resistance of the glass. The glass is heated to a uniform temperature and then quickly quenched with air, a process which amounts to rapid chilling. This creates compressive layers on the surface of the glass, increasing its impact- and thermal-resistance.

Hi Susan. I've been thinking about your post and what you say about the various differences between types of covers and heat conduction. Why I don't doubt what you say is true, I wonder if it is really a factor when the loaf is only being covered for the first 10 to 15 minutes?

An aside: I bet a pair of the silicone gloves would be a great at lifting off the hot pyrex bowl.

--Pamela