Looking at glass

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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.

A puff of glass

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Fourth generation glassblower John Lehman makes a glass trap for a vacuum system as specified by chemistry professor John Gryder. Mr. Lehman and Dr. Gryder explain the process of making the glass piece, including "pulling points," using both cross fires and torch to heat the glass as it evolves. A brief film explores the history of glass, from volcanic obsidian to the man-made glass of the Egyptians. In 300 B.C. the blowpipe was invented, opening the way to new uses of glass. At the first American colony in Jamestown, Virginia, Captain John Smith built a glass factory. A film shows a reenactment of an early American glassblower making a bottle. Dr. Gryder displays historical tools still used in the art plus modern ones that have been added. Manufacturers of glass have changed the assumed properties of glass, making it pliant, strong, heat and cold resistant, etc. for new functions. Mr. Lehman completes the glass piece, inserts it in the vacuum system, and tests it for leaks.