Lead glass
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Lead glass is potassium silicate glass which has been impregnated with a small amount of lead oxide (from 12% to 28% by weight) in its fabrication. The lead is not intended to affect the glass's ability to transmit light; the result is to increase the refractive index of the glass, and thus its lustre, or sparkle. Its ability to refract light more efficiently than standard glass makes it an excellent material for prisms, decorative windows, and artificial jewelry.
Lead glass is used in fine tableware, particularly wine glasses and decanters. It was unknown until a few decades ago that alcohol stored in a decanter was capable of leaching the lead from the glass and contaminating the contents. While fine wine glasses are still made of lead glass, use of lead glass containers for the storage of alcoholic beverages of any sort is discouraged.
Lead glass's primary contemporary use is in the construction of televisions and monitors. In a standard cathode ray tube, high-energy electrons are fired at phosphors painted on the inside of the tube. This impact creates the visible light the monitor or tv screen produces; it also produces x-rays. The lead in the glass acts as a barrier to this unwanted radiation. Unfortunately, the amount of lead glass finding its way into landfills as a result of discarded electronic equipment may be more of a hazard than the radiation it is designed to block.