Looking at glass

This program originates from station WDTV in Pittsburgh, PA., and begins with a visual history of glass beginning with obsidian, natural glass. Lynn Poole shows the ingredients of glass: silica, soda, and lime. Dr. Davies, of the Mellon Institute, discusses the states of matter, focusing on solids. He then explains the random structure of glass and why lenses are made from this substance. Using a petrographic microscope, Dr. Davies shows three samples of glass fibers under both ordinary and polarized light. He notes that because the density of glass varies with temperature and within the same piece of glass, it breaks under pressure. He hammers squares of regular and tempered glass to show the difference in their shattering. Dr. Davies also demonstrates the chemical resistivity of glass and explains that because glass is a versatile solvent, it can be used to make such products as goggles for glassblowers. Also silver salt can be dissolved in glass to develop an inexpensive and wearable radiation meter.