Ten sharp facts about glass

obsidian

In my middle grade novel The Ice Castle, Daphne's friend Mr. Silica runs a glass factory that plays an important role in the story. As I poked around researching the book, I learned a lot of fascinating tidbits about glass.

1.   The definition of glass is "an amorphous solid," which means a solid with no crystal structure, where the atoms and molecules are arranged more or less at random.

2.  Volcanic glass is created when magma cools suddenly, not allowing crystals to form in the cooling rock.  One common form of volcanic glass is obsidian, black, smooth, and shiny.

3.  Another natural form of glass is found in fulgurites -- glass tunnels made when lightning strikes sand and heats it to its melting point. The Museum of Science in Boston has a fulgurite many feet long.

The sand cast of a fulgurite several inches long

Fulgurite - see the glassy inner surface

4.  The earliest glass was made in Mesopotamia and Egypt in 3500-2500 BCE.  Early glass beads may have been formed accidentally as sand melted in the slag heap of furnaces for purifying metal.

5.  The Romans were probably the first to use glass for windows, around 100 CE.  Glass windows did not become common in ordinary houses in England until about 1500 years later.  Other houses still used animal horn to keep the cold out while allowing entry of some light.

Tinted float glass

6.  The most common form of manufactured glass today, soda lime glass, is made up mostly of silcon oxide, or sand.

7.  To make large flat panes, molten glass used to be poured and allowed to spread on a flat surface, which led to the glass being thicker in the middle.  To address this, glassmakers spun the flat surface, leading to thicker glass around the edges.

8.  Today, flat panes of glass are often made by the "float glass" method, in which molten glass is floated on another liquid surface, such as molten tin.  Gravity smooths and flattens the glass.

9. Manufactured glass can be colored, but it is valued for its transparency.  About 92% of the light that falls on a pane of clear glass passes right through.

10.  "Gorilla Glass," first developed by Corning in the 1960's and perfected for Apple products, is a strong, hard, flexible glass that is difficult to scratch.  Gorilla glass is now used in hundreds of millions of mobile phones, computer displays, and other screens.

Gorilla Glass from Corning

Glass, from skyscraper windows to contact lenses, is an amazing bit of technology that has been part of our lives for millennia and yet continues to improve.  In The Ice Castle, ambitious Itzo Silica worries whether he can improve his technique enough to fill a mysterious order from the Palace of Music...but he won't reveal to anyone what the order is for.