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Glass Class

Uncommon knowledge about an extraordinary material


Since 1851, scientists have had a love affair with glass. They've been fascinated by its properties, by manipulating those properties to solve real-world challenges, and by pushing the boundaries of what is possible to find new applications for this amazing, strong, and versatile material.

In this piece, Dr. Peter Bocko describes the many wonders of glass that keep scientists motivated to continue innovating.

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Dr. Peter Bocko explains passion for glass.

Fact 01

While many elements and compounds can form glasses, nearly all conventional glasses (in fact, all glasses that you have likely encountered) are based upon one of the most versatile chemical families: the silicates — i.e. materials based upon SiO2.

foreground SGC Group
SGC Group
SGC Group

Fact 02

90% of the Earth's crust, and almost 50% of the mantle, is silicate. In fact, looking at the big picture from the unique perspective of the glass chemist, the entire biosphere (all the people, animals, plants, and bacteria) amounts to less than a one part per trillion carbon- based layer on top of a diverse, pristine silicate planet.

Fact 03

Glass objects are among the oldest man-made materials, perhaps dating before 3400 B.C. Moreover, natural glass objects are among the oldest found in the solar system. Scientists found tiny silica glass spheres in lunar soil brought back by Apollo astronauts that were three billion years old.

SGC Group
SGC Group

Fact 04

The ultimate theoretical strength of glass exceeds the herculean level of 10 Gigapascals (GPa), a level few crystalline materials can achieve. Simply said, glass can take a hit.

Fact 05

Glasses are stable over time; in fact, exceedingly so. Keying off the common misperception that glass is actually just a supercooled liquid, a persistent myth is that the glass windows in medieval cathedrals are slightly thicker at the bottom than at the top because of infinitesimal glass flow over the centuries.

Glass scientists have calculated that it would require 20 trillion times the age of the earth to create a visible thickness change in a glass window.

Fact 06

Obsidian, a naturally occurring volcanic silicate glass, has been used by man since the Stone Age because of its ability to be fractured to create a super-sharp cutting tool. Obsidian is still used today in specialty surgical blades that have a cutting edge many times sharper than highest-quality steel surgical scalpels. The cutting edge of an engineered obsidian blade is only about three nanometers thick and much smoother than the finest sharpened surgical steel.

Surgical Blade (Steel)

Obsidian Blade

Fact 07

Although silicon and oxygen are the predominant constituents of glass, silica is also a gracious collaborator with its friends on the periodic table. A survey of glass research reveals more than 50 other elements that have been used as additives to silica glass in order to create glasses with unique physical, thermal, or optical properties for a wide variety of technical and artistic applications.

Fact 08

Glass is remarkably useful as an engineering and artistic material because its viscosity (resistance to flow) decreases in a smooth and continuous manner with increasing temperature, unlike crystalline materials that have abrupt transitions from solid to liquid. This property allows the glass worker to heat a glass to just the right temperature so she has the right consistency to mold, cast, blow, draw, sag, etc., to create a useful or artistic shape.

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Fact 09

Glass is one of the most transparent materials known to man. Glass used in optical fiber has 30X the transparency of the purest water, and only about 1% less transmittance than air on a clear day. An optical fiber's capability to transmit digital optical signals undistorted over great distance has made it the foundation of our information society.

Fact 10

One of the most ubiquitous high-tech glasses is the LCD substrate. In 2012, the LCD industry is expected to require 3.6 billion square feet of glass — enough to cover the entire length of National Highway 8 from Mumbai to Surat with a ribbon of glass four lanes wide, including a generous allowance for shoulders and median.

Fact 11

Glass has been used for millennia as a container because of its effectiveness at keeping contents (such as a liquid or a gas or even a high vacuum) completely isolated and protected from contamination by the surrounding environment. A molecule of oxygen, for example, takes about two weeks to pass through a 1mm thickness of polycarbonate polymer (a common "high-tech" plastic). The same oxygen molecule would take 30 billion years to pass through 1mm of silica glass!

Polycarbonate Polymer


Silica Glass

Fact 12

Silica glasses get their stability and strength from a continuous network of Si-O-Si bonds (a.k.a. the Siloxane Bridge). This is the core reason why silica glass can create objects of great utility and beauty that endure for centuries, a time span in which metals corrode and oxidize and plastics turn to dust.

Light Bulbs

Art Glass

Optical Fibers

LCD Screens


"If you think glass is weak, think again... glass is used for the space shuttle's windows, for covering the tallest skyscrapers, in optical fiber cable buried in trenches under the ocean, and for bullet proof windows in combat vehicles. Glass has been designed into the most hostile environments known... as a re-entry heat shield for Apollo space capsules, to store the most reactive and noxious chemicals, as observation windows near the hot zones of nuclear reactors, and as a hull for a submarine under development to reach the bottom of the Mariana Trench. Why is it that glass fiber is used to reinforce engineering polymers and concrete, but never the other way around? Hmmm?
Glass is anything but weak."

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