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Glass: What's the Mystery?
by Jeanette Cain
Physicists and teachers find it difficult to classify and educate students on the properties of glass. It seems that glass is a fluid in only in one correct respect. Glass is regarded as a fluid when talking of the microscopic view. People believe that if something is a fluid, then it will flow. It is this point that causes the statement to be false when thinking of glass as a fluid.
Yvonne Stokes, a mathematician at the University of Adelaide, Australia, has proved with precise calculations that old stained glass windows could not have flowed in a perspective manner. Perspective can mean a view of things or facts in their correct relationship, and a drawing that shows the proper perspective of the object. Perspectiva is Latin resulting in "science of optics." Per is Latin for "through" and specere means "look." Naturally, put the two together and you will have "look through."
Stokes believes the myth survives since, "it contains a kernel of truth-and because glass is a confusing kind of matter." (Kunzig, p45) Glass is not the typical orderly arrangement of repeating crystal patterns. Glass is not crystallized as a liquid. Liquid and glass do not have a definitive line to separate them as a liquid and as a glass. Glass is formed by cooling a liquid below its freezing point. When cooled quickly enough, molecules are unable to organize into crystals. The liquid becomes sticky, like glue, when the temperature begins to drop. This results in the molecules being lazy, or slow moving.
Almost any liquid can become glass when quickly cooled, but some turn into glass easier than others. The more sticky a liquid is at its freezing point, the harder it becomes for molecules to organize into a crystalline shape, increasing the odds of it becoming a glass instead.
The glasses have been used in almost everything from telephone cables to Life Savers. Physicists, scientists, and researchers still cannot agree on the nature of glass. However, some researchers have suggested that an ideal glass could be produced if a liquid were cooled with geological slowness. It has been suggested that this type of cooling would somehow prevent the crystallization. Instead, the result would be one form at a certain temperature, not a solid hybrid as ordinary glass. It would have a definite phase of matter. The description of the ideal glass state is motionless, and almost as orderly as a crystal, yet not being a crystal. Needless to say, it is not known what this glass will look like, but it will need to be in a state of equilibrium.
Mark Ediger, chemist at the University of Wisconsin, describes this glass as, "A glass is constantly evolving, trying to get to equilibrium. A crystal is happy just to sit there, because it's already at the bottom of an energy valley. A glass is sitting on the side of a hill. And very, very slowly it does roll down." (Kunzig, p.46) Sounds a little like mankind's activities, don't you think?
If science is lucky, someone, somewhere, either in the first grade at school, or sitting in the hall of retirement, will discover the answer and the solution.
Sources:
1. Barnhart, Clarence L. Thorndike-Barnhart Comprehensive Desk Dictionary Doubleday & Company,Inc: NY. 1965
2. Kunzig, Robert. Discovery: "The Physics of...Glass." Discovery: USA. October 1999 issue. pps.45-46.
Further Study:
The Physics of...Glass
Article by Robert Kunzig in Discover Magazine October 1999.
Is glass liquid or solid?
Article explaining the properties of glass.
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