Lead Crystals
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 Ceramics
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 cermet.
ceramic products have been hard, porous and brittle.
