Pyrex Wonders

pyrexGlass is made by mixing and heating silica (sand), sodium carbonate (soda) and limestone (calcium carbonate).  But, as we know, glass breaks quite easily, especially when subjected to sudden changes in temperature.  Pour hot liquid into a cold glass, and often the liquid ends up on the floor.  However, if a little boron (in the form of borax), is added to the mix, the resulting glass becomes shatterproof and expands and contracts much less with temperature change.  The first such glass was produced in Germany by Otto Schott back in 1884, although there is a popular, but probably apocryphal, story about a Roman glassmaker who somehow accidentally hit upon the secret of unbreakable glass in the first century AD.  By that account Emperor Tiberius was presented with a sample of “vitrum flexile,” which its inventor hurled to the ground without breaking it.  Tiberius was amazed.  And he immediately had the hapless glassmaker put to death, fearing that the new-fangled glass would make his own gold and silver dishes less valuable.  The story probably isn’t true, but could be.

Glass was well known to the Romans and borax (sodium borate) does occur naturally, so it is not inconceivable that a glassmaker could have added borax to glass just to see the effects.  While the Tiberius story may be suspect, we do know for sure that the details of making borosilicate glass were worked out by the Corning Glass Works Company in the early 1900s.  Railroad workers at the time had a problem with their lanterns.  If a hot lamp was struck by rain or snow, the glass would often shatter.  Corning exploited Otto Schott’s discovery, added boron compounds to the glass mix, and came up with lantern globes that would not break if suddenly cooled.  And then came an epic moment.  The wife of one of the company’s scientists became annoyed when a new glass casserole she had purchased broke after putting it in the oven.  Knowing about her husband’s work with glass, she asked him to bring home a sample of the new “unbreakable” variety.  The company had no casseroles of course, but they did make some battery jars, and it was a simple matter of sawing a couple of these in half.

It was in one of these makeshift pans that Bessie Littleton baked a historic sponge cake.  The cake baked quickly, didn’t stick to the glass, and was of a uniform color.  Mr. Littleton reported his wife’s experiment and the rest, as they say, is history.  Corning decided to get into the consumer market, and within two years came up with a line of shatterproof kitchen products.  Since the first dishes were destined for baking pies, the name Pyrex was chosen for the new-fangled glass, replacing the letters “ie” with “y” for esthetic reasons.  Women fell in love with Pyrex, and by 1919 over 4.5 million dishes had been sold.  And then scientists discovered Pyrex.  Here was an ideal material for test tubes, flasks and other equipment that had to endure repeated heating and exposure to corrosive substances in the laboratory.  Go into any lab today, and you will be surrounded by the wonders of Pyrex.

Joe Schwarcz

3 responses to “Pyrex Wonders”

  1. Em says:

    interesting background, but a post about the science of Pyrex should really touch on the recent changes… pyrex cookware isn’t made the same way any more, and does in fact seem to be somewhat more sensitive to changes in temperature

  2. Aubrey Jon Erickson says:

    Don’t confuse tempered glass with boro-silicate glass.

  3. Owen Funnell says:

    surely domestic Pyrex is no longer borosilicate, but tempered, glass which when breaking shatters.b

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