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The pyrex glass controversy that will not die

Clear Glass Pyrex cookware is virtually an American icon. These famous clear pans, with their pleasant weight and remarkable resistance since 1915, are indispensable for cooking biscuits, casseroles and pies. There's only one problem. About 15 years ago, the pans began to explode when they got too hot – which is ironic, as Pyrex glass was specifically designed for heat-resistant properties. Some accused a change of glass formula and flocked to thrift stores to buy older models. Others were joking. Everyone agrees that exploding glass is bad.

Pyrex made headlines recently because its parent company took a big step forward. Corelle Brands, the parent company of Pyrex, plans to merge with, among others, Instant Brands, the maker of the very popular instant pot. The terms and conditions have not been disclosed and it is unclear how the merger affects the company's products. However, the news is reminiscent of the centuries-old controversy that comes with popular glass pans, violent explosions, and some gnarled injuries. Pyrex is also the subject of a class action lawsuit in Illinois. Corelle Brands, the parent company of Pyrex, insists in judicial records that breakage is due to customers not using their products properly. More about this case in a minute.

To understand the Pyrex controversy, you need to look at the explosion reports in the context of the history of the glass. Not the whole history of the glass, of course, but a series of innovations that began with Otto Schott, a German scientist who invented a new type of glass in the late 1

9th century. This so-called borosilicate glass was not only heat-resistant, but also withstood sudden temperature fluctuations. Corning Glass Works developed its own recipe for borosilicate glass in 1908. Corning employee Jessie Littleton discovered a new use for the material after his wife Bessie had used a cut-off borosilicate glass battery to bake. Seven years later, Pyrex cookware entered the American market. The company referred to its products as "fire protection glass" in early ads.

These data are important because the Corning patent for borosilicate glass used to make Pyrex pans expired in 1936. At that time, the company developed a new formula for aluminosilicate glass, from which a series of frying pans called Pyrex Flameware was made. (This line was discontinued in 1979.) The actual roots of the current controversy were laid in the 1950s, when Pyrex began making cookware out of hardened soda-lime glass. Corning licensed the Pyrex brand in 1998 to a company called World Kitchen – now Corelle Brands. In almost all countries, all Pyrex cookware sold in the US this year was made from tempered soda lime glass. This is where the controversy gets really hot.

The vast majority of glassware consists of soda-lime glass: windowpanes, glasses, bottles and all types of glass. Soda lime glass is cheaper than borosilicate glass, which is why Pyrex undoubtedly experimented with it. However, borosilicate glass is not only harder, stronger and more durable than soda-lime glass; It is also more resistant to thermal shocks. Thermal shock is what happens when a temperature change causes different parts of a material to expand at different speeds and the resulting stress can cause the material to rupture. When the temperature changes quickly, materials such as glass can shatter or explode. Resistance to thermal shock is one of the reasons why Pyrex has become so popular with cookware. You could put a hot glass pan in a cool place without worrying about it shattering or breaking. This is also one reason why laboratories prefer to use borosilicate glass rather than conventional soda-lime glass. Pyrex cookware currently sold in the US undergoes a thermal tempering process. Theoretically, the glass should be strengthened.

In practice, the difference between the performance of borosilicate glass and soda-lime glass is significant. When asked about the science behind the glass, Dr. John C. Mauro, a professor of engineering and materials science at Penn State University, e-mailed that the coefficient of thermal expansion (CTE) is the main parameter used to measure thermal shock resistance. A higher CTE number means that the material is less thermally sensitive. For example, Corning Visions cookware, a precursor to Pyrex Flameware, is designed for use on hot plates and has a CTE close to zero, Mauro explained. Borosilicate glass has a CTE of 3 or 4 parts per million per 1 Kelvin change (ppm / K). Soda lime glass, however, has a CTE of 9 to 9.5 ppm / K.

"The advantageous qualities of soda-lime silicate glass are that it is extremely cheap yet has fairly high chemical resistance and good optical transparency," explains Mauro. "Soda lime silicate has a poor temperature shock due to its high CTE. … borosilicate glass withstands 2.5-3 times the temperature difference compared to soda lime silicate. "

Mauro knows his glass too. Before joining his faculty position at Penn State University, he worked for Corning for almost two decades, where he was one of the inventors of Gorilla Glass. It is worth noting that Corning was the birthplace of Pyrex. Mauro has also written scientific papers on pyrex glass chemistry and is editor of the Journal of the American Ceramics Society. Mauro makes the science behind soda-lime glass and heat sound even more harmful due to its extensive knowledge of materials. He discovered how soda-lime glass is tempered to improve its strength. By this tempering, however, the interior of glass is compressed more strongly.

"When it breaks, it breaks catastrophically (ie, it breaks many small pieces, so-called" fragility "), Mauro said." This contrasts with an uncured borosilicate glass compared to a tempered soda lime would break into much larger pieces. "

Photo: Wikicommons

Perhaps it was true then that borosilicate glass to soda lime glass became a big deal for Pyrex enthusiasts.Many believe that the new tempered soda lime glass will be more susceptible to temperature changes Explosions is a belief supported by a basic science, and World Kitchen, which claims to be responsible for the shift, insists that the tempering process is so good that the difference in glass types does not matter, and Corning executives have since claimed that For years, Pyrex made of borosilicate glass and soda lime glass before giving the brand to World Kitche This has not stopped Pyrex buyers from searching the Internet, selling real estate and second-hand stores around the world looking for Borosilicate Pyrex. A website even shows how different graphics and origins are safer for Pyrex products. (Protip: Look for All-Caps PYREX graphics that point to either Vintage or Europe, where a company called Arc International owns the Pyrex brand and still makes its borosilicate cookware.)

How much older ( or European) Borosilicate Pyrex is being debated as the new soda lime glass Pyrex. Exploding Pyrex incidents have occurred since the takeover of World Kitchen. In a much-cited 2008 Consumer Affairs survey, some pretty crunchy reports were made by people doing simple things, like putting a hot pyrex pan in the oven just to make them explode in their hands and burning broken glass in to send their tags. There are also photos of the injuries, so click through the report. At that time, World Kitchen denied any responsibility for the incidents and stated that "Explosion reports make up an extremely small percentage of the 370 million Pyrex dishes on the market and are often due to consumers not reading the instructions or not Consumer confuses a competitor's product with a Pyrex court. "Later, the company denied other aspects of the consumer affairs report.

The risk of explosion in glass cookware is also not limited to Pyrex products. Other companies also make soda lime cookware, which could make these pans and cups more susceptible to breakage or tearing. Pyrex parent company Corelle Brand – again the company formerly known as World Kitchen – said so as we asked about the exploding cookware controversy.

"Although glassware is at risk of breakage, Pyrex glassware has an exceptional safety record," said Corelle Brands spokesman in a statement. "Based on reports sent to the company and the Consumer Product Safety Commission, less than one-tenth of one percent of the millions of Pyrex products sold suffer a thermal break each year. Pyrex glassware has never been recalled. "

Corelle Brands also confirmed that some of its cookware had been made from soda-lime glass since the 1950s. However, when Consumer Reports examined the problem of breaking cookware in 2010, a Corning spokesman told the magazine that some of its factories made Pyrex from both borosilicate and soda-lime glass until Corning licensed the brand to World Kitchen. In other words: Buying a pre-1998 Pyrex cookware does not guarantee that it is made of borosilicate glass, and destroying it remains a risk.

In an email, the CPSC claimed to have received 850 reports of destruction or explosion over the past seven years. "Compared with the millions of glass cooking appliances used in consumers' homes, the number of incidents is low and the risk is low," said CPSC incumbent spokesman Patty Davis in an email.

But exploding pyrex incidents still happen and they happen again and again. After further reports of exploding and destructive Pyrex containers, Popular Science replicated an explosion incident in 2011 and showed in a video how minor burdens can lead to dramatic breakage events due to thermal shocks. Not long after, scientists from the American Ceramic Society conducted a study called "Shattering Glassware Cookware," which covered reports of explosions of cookware explosions, Pyrex. The authors of the article also examined the glass itself and discussed the chemical and practical aspects between borosilicate and soda-lime glass. "Soda silicate cookware is borderline," they concluded. "It does not seem to be appropriate for all household cooks."

After the study was published, Pyrex parent company World Kitchen sued the editor of the article and its author before the United States District Court for the northern district of Illinois. The company claimed that scientific research had made false and derogatory allegations about Pyrex cookware – especially its thermal break resistance – and asked the court to suppress the newspaper. World Kitchen finally lost the lawsuit on all counts.

Photo: Emily Lipstein (Gizmodo)

It's been 20 years since Corning licensed the Pyrex brand, and complaints about the breach have recently sparked litigation. Several Pyrex customers allegedly experiencing exploding glass incidents filed a class action lawsuit in June 2018 claiming that Corelle Brands warns consumers against thermal breakage and hides behind warnings and warranties when incidents occur. The court contains detailed information about the arguments and also contains some disturbing pictures. In December 2018, Corelle Brands filed a motion to dismiss the action. When we asked about the class action lawsuit, Corelle Brands said she did not comment on ongoing litigation.

The explosions continue, however. At around the same time as the class action lawsuit was filed, a Gizmodo employee himself exploded after microwave-cooling chilled black beans in a Pyrex container for a few seconds. The container exploded even though there were shards of glass in the microwave. To the best of its knowledge, it followed all safety instructions, but the situation resembles the defect of Pyrex products that others have pointed out. Even minor temperature changes can cause the glass to shatter or explode, and if that happens, the consequences can be dangerous.

The current Pyrex controversy is hard to draw conclusions just because we are not sure how many fractional events occur and under what specific circumstances. According to Corelle Brands, the parent company of Pyrex, the incidents are rare and attributable to abuse. However, many consumers believe that the risks are poorly communicated and the explosion can be unpredictable and dangerous. What seems crystal clear scientifically is that borosilicate glass is less susceptible to thermal shock than soda lime glass. It's also not hard to find, especially if you can live without the Pyrex logo on the bottom of your pan. Heck, Amazon Basics sells a pair of borosilicate glass pans for $ 15. The corresponding pyrex brand set of tempered soda lime glass costs $ 22. According to experts, the Pyrex glass can explode into small pieces. As unusual as these explosions may be, they sound bad.

This does not mean that you should throw away all your Pyrex cookware. However, you should follow the company's safety and operating instructions that you can find here. Here is an important quote from a long list of warnings: "Avoid sudden temperature changes on your glassware." That is, do not pour cold water into a hot Pyrex pan. Do not place a hot pyrex pan on a cold marble slab. To avoid such things is not self-evident. But if you stick to the rules, that could mean the difference between a delicious cooked casserole in an intact Pyrex pan and an oven full of broken glass and leftovers. We can all agree that a delicious casserole is better than broken glass!

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