Lead crystal, (also called crystal), is Lead glass that has been hand or machine cut with facets. Lead oxide added to the molten glass gives Lead crystal a much higher index of refraction than normal glass, and consequently much greater “sparkle”.
Decorative Lead crystal glass is one of the most attractive forms in which Lead is used. Normally added in the form of Lead oxide at 24-36%, it adds luster, density and brilliance to the glass. The glass is further enhanced by its ability to have decorative patterns cut on it and has the characteristic ring associated with Lead crystal. There is now a substantial market for a cheaper form of Lead ‘semi-crystal’ containing in the region of 14-24% Lead oxide and glasses are usually molded with the decorative pattern rather than hand-cut later.
Lead is also used in optical glasses (e.g. telescopes, binoculars), ophthalmic glass (e.g. spectacles), electrical glass (e.g. lamp tubing) and radiation protection glasses (e.g. for windows for radiation remote handling boxes, TV tubes).
Lead is used in a wide range of glaze formulations for items such as tableware (earthenware and china), wall and floor tiles, porcelain and some sanitary ware. The Lead compounds used are largely litharge, red Lead and Lead silicates. The advantageous properties offered by Lead compounds are lower melting points and wider softening ranges, low surface tension, good electrical properties and a hard wearing and impervious finish. Considerable research effort has been put into developing glazes with very low Lead release. Lead compounds are also used in the formulation of enamels used on metals and glasses.
Another important application for Lead compounds is in a range of ceramics (other than the glazes) used in the electronics industry. Typical of these are the piezoelectric materials such as the Lead zirconate / Lead titanate range of compositions known generally as PZI . These find a wide range of applications, such as spark generators, sensors, electrical filters, gramophone pick-ups, sound generators, etc.
A composite material of ceramic and metal is known as cermets. ceramic products have been hard, porous and brittle.