Trivia 084: A capital difference

A few weeks ago, I baked a cake for my friend’s birthday. His choice – a chocolate mousse cake – was something I had never made before. As part of the recipe, I had to melt some chocolate chips. One of the most common ways of doing this is by using a double boiler. To do this, fill a pot partway with water, and put it on the stove. Then, take a bowl that is slightly larger than the pot, and put it on top, ensuring that the bottom of the bowl is in the water. By doing so, you can apply a steady, even heat, without the risk of scorching what you’re cooking. This allows you to melt the chocolate without overheating it. There was just one problem – I did not have an extra metal bowl. So I simply used the next best thing – a Pyrex bowl.

Kitchen veterans should recognize the brand “PYREX“. Created in by the glass company, Corning Inc., this line of cookware is made of borosilicate glass. This special formulation of glass has a low coefficient of thermal expansion. This means that it does not expand much when heated or contract when cooled. As a result, it is ideal for glass cookware. If you take a normal piece of glass and heat it up, it might crack or shatter when cooled, especially if it is cooled too quickly. This is why you should always allow glass cookware to cool before washing it.

However, the glass used in Pyrex bowls and pans is able to resist such temperature changes, meaning that they can be used for baking and other high-heat applications. After its introduction in 1915, it quickly rose in popularity. Unfortunately, while borosilicate glass is completely safe, its production requires the use of boron, which requires special handling and disposal procedures. As a result, Corning Inc. began experimenting with tempered soda-lime glass in the 1940’s. Soda-lime glass is the same kind of glass that other products such as cups and windows are made out of. Tempering the glass using special heat and chemical treatments allows it to withstand changes in temperature almost as well as borosilicate glass.

And here’s where things get a bit confusing. In 1975, Corning Inc. trademarked the name “pyrex“. Before this, their products were marketed as “PYREX“. The only difference between these names, of course, being the capitalization. The PYREX trademark was eventually licensed to companies in Europe, Africa, and the Middle East, while pyrex is still used in the United States, South America, and Asia. In the US, cookware sold under the pyrex label is now entirely soda-lime glass. However, PYREX made in Europe (specifically at their plant in France), is still made out of borosilicate glass (such as this roasting pan).

Despite many (1, 2, 3, 4, 5) articles online claiming that PYREX is made out of borosilicate glass and pyrex is not, it’s unfortunately not quite that simple. Corning Inc. introduced soda-lime glass products decades before they began using the pyrex trademark. And although PYREX glass made in France is still borosilicate, I could not find information about other areas – Africa and the Middle East. So it is possible that soda-lime PYREX products are still being made. Therefore, here is my rule of thumb: If your cookware says “pyrex“, it is almost certainly soda-lime glass. As far as I can tell, nobody makes borosilicate glass cookware under this trademark. If you have some antique PYREX, it may or may not be borosilicate, depending on when and where it was made. If you purchase PYREX today from France, it will be borosilicate glass.

With all that said, both kinds of glass can shatter if they are heated and cooled too quickly. Therefore, it is always best to be careful when handling hot glassware and allow it to cool gently, and never put it under the broiler. If you still want to cook with borosilicate glass, you don’t need to travel all the way to France. Most laboratory-grade glassware is made out of borosilicate glass. You also get the added benefit of getting to cook with beakers and stuff. In the case of my chocolate cake, the application of heat was slow and gentle, so everything was fine. The only problem is that the cake was very large, and we still have half of it in our fridge.

Yes, this post is a day late. That’s because I was working on a new timelapse, and I wanted to be able to share it with this post. You can check it out here! I got a pretty decent view of Seattle at night. It’s not quite what I was looking for, but it ended up being pretty nice. I even managed to capture the International Space Station going overhead.

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