Lightning also has the power to make glass.

When lightning strikes the ground, it fuses sand in the soil into tubes of glass called fulgurites.

L. Carion/Carion Minerals, Paris

When a bolt of lightning strikes a sandy surface, the electricity can melt the sand. This melted substance combines with other materials. Then it hardens into lumps of glass called fulgurites. (Fulgur is the Latin word for lightning.)

Now, scientists are studying fulgurites in Egypt to piece together a history of the region’s climate.

Thunderstorms are rare in the desert of southwest Egypt. Between 1998 and 2005, satellites in space detected hardly any lightning in the area.

Amid the region’s sandy dunes, however, fulgurites are common. These lumps and tubes of glass suggest that lightning used to strike there more often in the past.

Recently, scientists from the National Autonomous University of Mexico in Mexico City studied fulgurites that had been collected in Egypt in 1999.

When heated, minerals in fulgurites glow. Over time, exposure to natural radiation causes small defects in the glassy fulgurites. The older the material is, the more defects there are, and the stronger the minerals glow at certain wavelengths of light when they’re heated. By measuring the intensity of the glow when the samples were heated, the researchers found that the fulgurites formed around 15,000 years ago.

The gases trapped in bubbles within samples of fulgurite provide clues to ancient soil and atmospheric chemistry and climate.

Rafael Navarro-González

The scientists, for the first time, also looked at the gases trapped inside bubbles in the glass. Their chemical analyses showed that the landscape could have supported shrubs and grasses 15,000 years ago. Now, there’s only sand.

Today, shrubs and grasses grow in the hot, dry climate of Niger, 600 kilometers (375 miles) south of the Egypt site. The researchers suspect that, when the fulgurites were created, the climate in southwest Egypt was similar to present-day conditions in Niger.

Fulgurites and their gas bubbles are good windows into the past, scientists say, because such glasses remain stable over time.

Analyzing the Egyptian fulgurites, in particular, is “an interesting way of showing that the climate in this region has changed,” says Kenneth E. Pickering, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Even if you’re afraid of thunderstorms, the amazing powers of lightning are bound to impress you! And lightning strikes can even tell a story of ancient times.—E. Sohn

Going Deeper:

Perkins, Sid. 2007. Stroke of good fortune: A wealth of data from petrified lightning. Science News 171(Feb. 17):101. Available at http://www.sciencenews.org/articles/20070217/fob5.asp .

You can learn more about fulgurites at en.wikipedia.org/wiki/Fulgurite (Wikipedia).

Goggles that fog up while you’re skiing can be a nuisance—maybe even dangerous.

The problems of fogging and glare don’t seem to have much in common. But materials scientists are finding that they can solve both problems at the same time. The secret is to put a coating with the right combination of chemicals and texture on the surface of the glass or plastic.

Clearing up fog

Fog forms on a mirror or window when water vapor in warm, moist air condenses to create tiny water droplets on the smooth, cool surface. Instead of letting light through, the droplets tend to scatter light in different directions. This makes it hard to see through the glass. What you do see looks blurry.

To deal with this problem, Michael Rubner considered the way droplets form on surfaces with different textures. He’s a materials scientist at the Massachusetts Institute of Technology.

Like many researchers who work on materials, Rubner was inspired by nature. In this case, he looked at the leaf of the Japanese lotus flower, which causes water to bead into rounded droplets (see “Inspired by Nature” and “Butterfly Wings and Waterproof Coats“).

A lotus flower and leaves with water droplets.

U.S. Fish and Wildlife Service

The surface of a lotus leaf is waxy and filled with tiny holes, so it looks a bit like a sponge. The waxy substances on the leaf’s surface repel water. At the same time, air trapped in the holes keeps water from sticking.

To create a coating that prevents fogging, Rubner’s idea was to replace the waxy substances with chemicals that attract water.

Making a nanosponge

To make the new anti-fog coating, Rubner and his coworkers use a material called silica. Silica consists of the elements silicon and oxygen. It’s found in most kinds of rock, and it’s the main chemical compound in sand and glass. Silica also tends to attract water molecules.

The researchers work with tiny silica particles, each one just a few nanometers wide. A nanometer is one-billionth of a meter. In comparison, a human hair is about 80,000 nanometers wide. A nanometer-sized particle is much smaller than a living cell and can be seen only by the most powerful microscopes available today.

The scientists form the coating layer by layer by dipping a glass surface into a mixture of water and silica (or glass) nanoparticles, then into a mixture containing a type of plastic, or polymer. The plastic substance acts like glue, holding the glass particles together. The final coating has as many as 20 thin, alternating layers of polymer and glass particles.

The result is a coating with lots of air pockets—like a thin “nanosponge” made of glass, Rubner says. Yet, the particles and holes are so small that the coated glass still looks and feels smooth.

When exposed to warm, moist air, the coated glass surface attracts water. Instead of beading into rounded droplets, however, the water gets sucked into the holes all over the surface. This spreads out the water, and the resulting water film doesn’t scatter light in the same way that droplets do. You can still see through the glass.

A coated glass slide (left) shows the lotus flower clearly, while an untreated slide (right) fogs the view.

Rubner

A glaring improvement

The new coating also changes the way in which light interacts with glass. Light moves very quickly, but it moves more slowly through glass than through air. Because of this mismatch, when light hits glass, some of it reflects off the surface, leading to glare.

Because of the air pockets within the spongy coating, the coated glass surface acts like a mixture of glass and air when light hits it. This combination means that almost all of the light goes through the glass. Very little light is reflected. There’s no more glare.

In addition to improving Game Boy screens, this type of coating could lead to better windows for greenhouses, Rubner says. In a greenhouse with coated glass that reduces glare and resists fogging, more light gets in, so plants have more light for growth.

Stronger coatings

A coating isn’t practical if it scratches or rubs off easily, however. To make the materials more durable, Rubner and his team heat the coatings to a high temperature, about 500 degrees C.

Heating works fine for glass, but heated plastics will melt or even burn up. So, at this point, only materials that can stand high temperatures can be coated with the new anti-fog and anti-glare film.

Although it hasn’t been done yet, constructing a greenhouse using improved glass that cuts glare and resists fogging would allow more light into the chamber.

Peggy Greb, Agricultural Research Service, U.S. Department of Agriculture

In Australia, Paul Meredith and Michael Harvey of the University of Queensland have taken a similar approach. They also use porous silica—a thin layer of glass filled with tiny holes—as a coating. But their procedure for creating the coating is somewhat different.

Meredith and Harvey have even solved the problem that Rubner and his group are still working on. Their porous silica coatings are durable on both plastic and glass. The two researchers have formed a company, called XeroCoat, to make such coatings for solar cells.

In 2 to 5 years, you might be shopping for improved eyeglasses or ski goggles or riding around in a car with a windshield that resists fogging and reduces glare. It’d be a new window on the world, thanks to materials research.

Going Deeper:

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Now, researchers from London and Germany have found evidence that the Egyptians were making their own glass as far back as 3,250 years ago. The discovery defies a longstanding theory that ancient Egyptians imported glass from Mesopotamia.

Archaeologists have found a variety of items used in glassmaking, including this ceramic container, at an ancient Egyptian glass factory. Glass was colored and heated in this vessel, which is about 7 inches across. The inset shows glass ingots from a Bron

© Science

The oldest known remnants of glass come from an archaeological site in Mesopotamia. The shards are 3,500 years old, and many experts assumed that this site was the source of fancy glass items found in ancient Egypt.

The new evidence, uncovered in an Egyptian village named Qantir, however, shows that an ancient glassmaking factory had operated there. Artifacts from Qantir include pottery containers holding glass chunks, along with other traces of the glassmaking process.

This piece is all that remains of a clay funnel used to help pour glass powder into a ceramic vessel.

© Science

Chemical studies of the remains suggest how the Egyptians made their glass, the researchers say. First, the ancient glassmakers crushed quartz pebbles together with the ashes of burnt plants. Next, they heated this mixture at low temperatures in small clay jars to turn it into a glassy blob. Then, they ground the material into powder before cleaning it and using metal-containing chemicals to color it red or blue.

In the second part of the process, the glassworkers poured this refined powder through clay funnels into ceramic containers. They heated the powder to high temperatures. After it cooled, they broke the containers and removed solid disks of glass.

Egyptian glassmakers probably sold and shipped their glass to workshops throughout the Mediterranean. Artisans could then reheat the material and shape it into fancy objects.

This map shows the Egyptian village Qantir, where a glass factory was located, and trade routes that would have carried glass from the Nile Delta to other parts of the Mediterranean.

© Science

Now that glass is so easy to come by, it might be hard to imagine how special it was back then. At the time, wealthy people exchanged sculpted glass pieces as a way to make political bonds with each other. If you hand someone a piece of glass today, they’d probably just toss it in a recycling container!—E. Sohn

Going Deeper:

Bower, Bruce. 2005. Ancient glassmakers: Egyptians crafted ingots for Mediterranean trade. Science News 167(June 18):388. Available at http://www.sciencenews.org/articles/20050618/fob3.asp .