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THE LAMPS OF TIFFANY: Highlights from the Neustadt Collection |
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“By the aid of studies in chemistry and through years of experiments, I have found means to avoid the use of paints, etching or burning, or otherwise treating the surface of the glass…” –Louis Comfort Tiffany
While we often recognize great glassmakers such as Louis Comfort Tiffany for their artistic vision, we may neglect the fact that they were also chemists who spent endless hours experimenting to produce the perfect hues and textures in their glass. We, too, should be aware of the unique chemical properties of glass.
Physical Properties of Glass Deceivingly, glass appears to us as an ordinary solid material. However, it lacks the rigid crystalline structure that is characteristic of most solids. Though glass is strong and resists corrosion by all but the strongest acids and bases, it is a viscous[1] material: it flows like a liquid. For example, consider the windows of a very old house. Often, the glass of these windows becomes thicker at the bottom because, over time, gravity has caused the glass to flow downward. Glass is also elastic, meaning that it can be bent or stretched somewhat and return to its exact original shape. This can be observed in a large window on a very windy day, when the glass appears to heave and creak within the window frame with each gust. If glass is stretched or bent beyond its strength, then it will shatter. Though glass is neither liquid nor solid, it exhibits properties of both states of matter.
Composition of Glass The three components of glass are formers, fluxes, and stabilizers. Formers are the basic materials that can be melted and then cooled into glass. The most common former is sand, which is rich in a chemical compound called silica, also known as silicon dioxide (SiO2). Fluxes are added to the former to help it melt at a lower temperature than it would alone, although this temperature is often well over 2000° Fahrenheit. Standard fluxes are soda ash and potash. Stabilizers, such as limestone or magnesia, are added to keep finished glass from crumbling.
Making Colored Glass Color in glass is a function of chemistry. By adding various metal oxides, glassmakers can create different colored glasses. In a series of difficult experiments, Louis Comfort Tiffany added metal oxides to batches of clear molten glass to produce the exact tones he desired so that he could create a vast spectrum of colors and “paint” with glass. Here are the results of his and other chemists’ experiments:
Cupric oxide " blue Iron oxide " green Manganese oxide " purple Gold, copper or selenium " red Coke, coal or carbon oxides " amber Manganese + cobalt + iron " black
Iridescent glasses, such as Tiffany’s Favrile and Carder’s Aurene, are produced through a complex chemical process. First, rare metal compounds are added to molten glass while the glass is subjected to a flame. Each metal produces a different color effect, such as blue or gold. Then, the glass is sprayed with chloride (Cl2), which causes fine lines to erupt all over the surface. These lines pick up the light and produce a shimmering appearance.
Shaping Glass Glass blowing is the most common method of producing different shapes in glass. Glass is heated in a furnace to the working point, at which the glass will neither melt completely nor harden. The glass blower gathers the molten glass at the end of a hollow blowpipe and inflates it like a bubble. Then the glass can be blown into a mold or freely shaped at the end of the blowpipe using simple tools. Once the desired shape has been attained, it is important that the glass does not cool too quickly, because it may shatter. Therefore, the finished piece is annealed, placed in a 900° F oven that cools slowly. [1] For definitions of words in bold print, please see the Glass Glossary. |
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