Composition of Lead Crystal Glass

Composition

• Normal glass is a mixture of mostly silica, sodium oxide and calcium oxide. In lead glass, however, the chemical lead (II) oxide (PbO) is added. The amount of lead can vary, depending on the glass properties desired and the intended use. Lead levels as low as 2 percent by weight are found in some types, but the level of lead in crystal glass intended for show purposes is generally in the range of 24 percent or higher.

History

• The invention of leaded crystal glass is attributed to the Englishman, George Ravenscroft, around 1676. At the time, Ravenscroft was trying to find new methods of glass production that would allow him to match the success of the glass makers of Venice. He experimented with using flint as the silica source to make glass but found this resulted in poor-quality glass. Ravenscroft was able to improve the glass by adding high percentages of lead, resulting in lead crystal. He immediately recognized the desirable nature of the resulting glass and patented his invention.

Properties

• The primary special quality of lead crystal is its high refractive index. This means that lead crystal bends light at sharper angles than normal glass, resulting in a brilliant, sparkling effect, especially when cuts are made in the glass. Lead crystal also has a prismatic effect, giving rainbow shades to its sparkle. As well, this type of glass is softer than normal, so it is easier to work with and can more readily be cast and cut into pleasing shapes.

Uses

• Lead glass with a high lead percentage is used largely for making crystal glass art objects, including vases, jewelry and small art objects such as sculptures. However, lead glass with a wide range of lead content is also used for many other purposes, including radiation shielding and glass solder.