Borosilicate Window

How much of the solar radiation that hits a transparent glass is actually heating the glass?

You have a transparent (borosilicate) glass window. Sun rays are falling on the glass, which is let's say placed horizontally. Some of the radiation passes through the glass, some is reflected back but some is absorbed and heats up the glass. How much of that total radiation is actually absorbed and makes the glass heat up? I speculate that would be somewhere around 2-3%. Any specialist in optics or heat flow?

The transmittance of good quality glass 1cm thick ranges from 99.6% to 99.9%, so the absorption is less than .4% in the visible spectrum. It increases in the ultraviolet. But if you have glass covering a box, nearly all the light passes through and heats whatever is in the box. The infrared energy radiated is mostly blocked by the glass. That's what heats a greenhouse.

Ginsberg Scientific 73029 Condenser Leibig Borosilicate 200mm $37.25 200mm long. Condenser Leibig Borosilicate glass. Straight Liebig style inner tube for easy cleaning. 200mm long.

Novara Black Ten-Light Flush Mount with Borosilicate Glass $430 Novara's organic nature evokes an intriguing sense of movement and fluidity. Graceful tentacles coated with a textural finish spiral away from the base in a free-flowing, abstract path that leads to delicate bulbs of borosilicate flat glass. An artful twist on the traditional chandelier, Novara brings a touch of whimsy to the room. -Glass/Shade: Borosilicate

Ginsberg Scientific 72084 Burette Borosilicate Glass With Teflon Stopcock PTFE 50ml capacitySub. .1ml $43.88 The high quality borosilicate glass burette with a Teflon stopcock is perfect of students because the stopcock is almost freezeproof. Capacity: 50ml.

Ginsberg Scientific 72083 Burette Borosilicate Glass With Teflon Stopcock PTFE 25ml capacitySub. .1ml $40.3 The high quality borosilicate glass burette with a Teflon stopcock is perfect of students because the stopcock is almost freezeproof. Capacity: 25ml.

ET2 Lighting E21900-10BK Novara 10 Light Flush Mount in Black with Borosilicate glass $199.06 Modern Contempo Flush Mount in Black with Borosilicate glass from the Novara Collection by ET2 Lighting. Dimensions: 15.75 H 30.00 W

ET2 Lighting E21901-10BK Novara 15 Light Ceiling Pendant in Black with Borosilicate glass $430.2 Contemporary-Modern Ceiling Pendant in Black with Borosilicate glass from the Novara Collection by ET2 Lighting. Dimensions: 24.75 H 30.00 W

Ginsberg Scientific 720810 Burette Borosilicate Glass With Ground Glass Stopcock 10ml capacitySub. .05ml $38.35 The straight bore stopcock burette has permanent and accurate graduation lines. Class A. Burette borosilicate glass with ground glass stopcock. Capacity: 10ml. Subdivision: 0.05ml.

Lock&Lock BOROSEAL Borosilicate Glass 8-pc Set $70.77 Capacity: 15.2 fluid ounces, 25.7 fluid ounces, 44 fluid ouncesMaterials: Heat-resistant GlassCare instructions: Wash with warm soapy waterCase of/pack of: Four (4) glass containers (with lids)Dimensions:Two (2) containers 5.4 inches wide x 5.4 inches long x 2.4 inches highOne (1) container 6.6 inches wide x 6.6 inches long x 2.8 inches highOne (1) container 7.9 inches wide x 7.9 inches long x 3.1 inches high

Lock & Lock BOROSEAL 7.8-inch 74.4-oz Borosilicate Orange Glass Pot $62.85 This Borosilicate orange glass pot is made with heat-resistant glass for a wide range of baking and cooking options. Attractive and practical, this piece will soon be a favorite in your kitchen.Dimensions: 7.8-inch diameterMaterials: Borosilicate heat resistant glassNumber of pieces: One (1)Care instuctions: Check for chips or cracks along the edge of glassware prior to use (if you find any chips or cracks, please return the item to the original store of purchase for a new one).Clean using a soft sponge and mild detergent.Remove lid and plastic inner support piece (included on some models) prior to use in oven. Do not use on direct open flame. To reduce the risk of damage to the item, do not over-expose to microwave or oven heat for extended periods of time and do not heat when empty.Always use oven mits or gloves when removign the pot from the oven.Fully defrost all frozen items before cooking to prevent damage and burns.Placing uncooled glassware in water or wiping with a damp cloth can cause damage. Please use caution.Lid may become slightly misshapen after microwave use, but will return to its original shape once cool.

Fisherbrand Disposable Borosilicate Glass Tubes with Poly Screw Cap, 16 x 150mm, 1000/cs $296.14 Features of the Fisherbrand Disposable Borosilicate Glass Tubes: Provides chemical stability and biological inertness of hard, borosilicate glass—at price of disposable tubes. Round bottom. Start clean—no lost samples due to contaminated, cloudy or scratched tubes. Avoid pH problems caused by soft glass. With natural linerless polypropylene screw cap and marking spot. Applications: Ideal for tissue culture, bacteriology, clinical chemistry, blood typing, and crossmatching procedures. No. Per Tray: 250.

Window $39.99 Titian Window - Giclee Print

Kimble Disposable Borosilicate Glass Tubes with Threaded End, 16 x 125mm, 1000/cs $399.4 Features of the Kimble Disposable Borosilicate Glass Tubes: Stand without support. For tissue culture work and general bacteriological use. Comply with ASTM* E 438, Type I, Class B glass requirements. Shrink-wrapped in modular trays. Without closures. GPI Thread: 15-415.

At the Window $39.99 Mary Cassatt At the Window - Giclee Print

A Window $19.99 Tina Jonsson A Window - Photographic Print

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Markoptics.com Mark Optics manufactures custom optical components such as quartz, borosilicate, germanium

Pyrex® Glassware: Is It Safe To Use?

The answer is complex—involving reports of flying glass and rebuttals calling “exploding” Pyrex® merely an urban legend.

Here’s the story: After hearing many frightening complaints about Pyrex® glassware that “exploded” during use, in 2008, Snopes.com had a Chicago TV investigative team research the matter to find out whether Pyrex® products were (in the words of stats.org) “weapons of glass destruction.” The resulting TV report left the strong impression that Pyrex® glassware was dangerous, and the matter got a lot of attention. Stats.org called the story “the second hottest urban legend on Snopes.com.”

True, the original Snopes.com report did contain some errors (later corrected), but the fact remains that hundreds of users have claimed that their Pyrex® glassware suddenly broke apart, in some cases shooting out sharp glass shards that caused injuries. These occurrences weren’t actually explosions, which, are caused by pressure from within (as happens when a bomb or balloon bursts). However, they were still scary, dangerous events. These incidents tended to occur when a glass dish was moved from the oven and placed on a counter (especially a cold, wet one), but there was also at least one report of breakage while the dish was still in the oven.

Pyrex® glassware has been on the market since 1915, and complaints about flying glass fragments are relatively new. So what happened? Originally, Pyrex® was made by Corning with borosilicate glass. Later, Corning began making some Pyrex® with adequately tempered soda lime glass before selling the name and the technology to World Kitchen. Since  the 1980s, Pyrex glassware produced in the U.S. has been made with soda lime. But the switch to soda lime itself was not the cause of the problem, as we learned.

In seeking the answer to “Is Pyrex® Glassware Safe?”, ShelfLifeAdvice.com contacted Dr. Sheldon Mostovoy, a metallurgist, Illinois Institute of Technology professor, and one of the scientists who tested the “new” (soda lime) Pyrex®. Here’s what he told us, “Borosilicate Pyrex® was much more heat resistant. The new Pyrex® was not adequately tempered. The tempering process is similar to the treatment auto glass gets to prevent shattering into sharp shards.” During Mostovoy’s experiments, he said, “The new Pyrex® shattered into sharp shards that were propelled many feet.”  Adequate tempering is extremely important because it 1) reduces the chances of sudden breakage due to thermal stress (from rapid temperature change) or mechanical stress (such as dropping the dish).  

Here’s what Mostovoy concluded: “I believe that, unless this issue of tempering the glass is corrected, there will be more people injured, even in cases where customers observe the company’s warnings.” Mostovoy recommends that World Kitchen either switch back to borosilicate glass or improve the tempering process on the soda lime glass.

You can play scientist and test your glassware yourself to see if it’s been properly tempered. Dr. Mostovoy says it’s easy. “I use a sheet of polarizing material but often just polarized sunglasses are enough. Take a Pyrex® dish, hold it up to the light, and look at it with polarizing plastic. If there are lots of colors, the dish has likely been properly tempered; if just a few colors show, it is likely poorly tempered.”

Does all this mean Pyrex® soda lime glassware is unsafe? World Kitchen denies this and has posted a page-long statement about the product’s safety record on the Pyrex® website. This statement does not respond to the concerns of scientists about inadequate tempering, nor does it indicate that any changes have been made in the manufacture of its products to make them more heat-resistant and less likely to “explode.”

Warnings about how not to handle Pyrex® come with the products and are on the Pyrex® website. Scientists working on the Pyrex® issue called the warnings inadequate because the print is too small and the contents too complicated, vague, and incomplete. Here are just SOME of the Pyrex® Safety and Usage Instructions:

• “NEVER use the product on top of a stove, under a broiler, in a toaster oven or place over oven vent or pilot light.”

• “Avoid severe hot to cold temperature changes.” (There are a number of specific warnings related to this general concept including not placing a hot Pyrex® dish on a cold, wet surface. In fact, the instructions probably don’t say so, but the safest way to handle a hot Pyrex® dish is to place DRY pot holders or a towel between the dish and the counter. Even a room temperature counter may provide sufficient temperature change to cause breakage.)

• “ALWAYS add a small amount of liquid to the vessel prior to baking foods that release liquids while cooking.” (What’s a small amount? Which foods release liquid? How much is sufficient?)

• “DO NOT use or repair any item that is chipped, cracked or scratched.” (Is the user supposed to scrutinize the dish with a magnifying glass before each use, looking for defects? Should I throw out the dish if it has even a small scratch? Incidentally, if you are nesting two or more Pyrex® dishes, they’re more likely to get scratched, but the instructions may not say so.)

If you can keep all of the company’s warnings in mind or are willing to post them in your kitchen, you will decrease the odds of having an explosive accident with Pyrex®. (But, Mostovoy reiterates, without proper tempering, “window glass” dishes can break even when all the cautions are observed.) Some of these warnings tell you what you’ve probably known for many years. Most people know that glass items can’t tolerate rapid temperature change. And who would try to broil a steak in a glass container?

If, after reading this far, you feel uneasy about using Pyrex® bakeware, consider the alternatives suggested by Barb Randall in WestLinn Tidings: “A quick tour of a local kitchen supply store showed many options, including foil, tin, metal…, ceramic…, and porcelain….”

Sources:

http://shelflifeadvice.com

Email exchanges with Dr. Sheldon Mostovoy, metallurgist, Illinois Institute of Technology and expert witness concerning Pyrex® glassware

Chicago CBS affiliate TV station, news reports by Pam Zekman: “The Trouble with Pyrex,” 2008.

Snopes.com “Exploding Pyrex”. http://www.snopes.com/food/warnings/Pyrex.asp

Stats.org Stats Articles 2009 “Exploding the exploding Pyrex rumor" http://stats.org/stories/2009/exploding_pyrex_oct14_09.html

WestLinnTidings.com “Exploding Pyrex is an urban legend” http://www.westlinntidings.com/features/story.php?story_id=125797193759322700

Pyrexware.com “Setting the Record Straight: The Truth About Pyrex” http://www.Pyrexware.com/thetruthaboutPyrex/index.htm

About the Author

ETHEL TIERSKY, the editor and frequent author for http://shelflifeadvice.com, has been a free-lance writer since 1963 and a food safety fanatic for even longer. She has published dozens of magazine articles and co-authored 14 grammar texts and readers for adults studying the English language. Developing http://shelflifeadvice.com has kept her busy since retiring from her teaching position as associate professor of English at Harry Truman College in Chicago. Some of her other writings for the site include “Don’t Let Those Food Expiration Dates Scare You,” “FAQs on Food Product Dating,” and product write-ups on mayonnaise and water.