Lead glass

Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass typically contains 18–40% (by mass) lead(II) oxide (PbO); modern lead crystal or leaded crystal, historically also known as flint glass for the original silica source, contains a minimum of 24% PbO. Lead glass is desirable for a variety of uses due to its clarity. In marketing terms it is often called crystal glass.

The term lead crystal is, technically, not an accurate way to describe lead glass, because glass lacks a crystalline structure and is instead an amorphous solid. The use of the term remains popular for historical and commercial reasons but is sometimes changed to simply crystal because of lead's reputation as a toxic substance. It is retained from the Venetian word cristallo to describe the rock crystal (quartz) imitated by Murano glassmakers. This naming convention has been maintained to the present day to describe decorative holloware.

Lead crystal glassware was formerly used to store and serve drinks, but the health risks of lead have made this use rare. An alternative material is modern crystal glass, in which barium oxide, zinc oxide, or potassium oxide are employed instead of lead oxide.

In the European Union, labelling of "crystal" products is regulated by Council Directive 69/493/EEC, which defines four categories, depending on the chemical composition and properties of the material. Only glass products containing at least 24% lead oxide may be referred to as "lead crystal". Products with less lead oxide, and glass products with other metal oxides used in place of lead oxide, must be labelled "crystalline" or "crystal glass".