Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by mass) lead(II) oxide (PbO), while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO. Lead glass is often 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 term to describe lead glass, because glass lacks a crystalline structure and is instead an amorphous solid. The use of the term lead crystal remains popular for historical and commercial reasons, and sometimes simply crystal because "lead" seems toxic to consumers. 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 hollow-ware.
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