The defining feature that separates lead crystal from crystal glass is the object's lead content. Lead crystal contains between 24 percent and 35 percent lead, while crystal glass is made by replacing lead with zinc oxide, potassium oxide or barium oxide. The lead in lead crystal increases the refraction of light through the glass and its density, giving the object more appeal as a fine glass.
The technique of manufacturing lead crystal was first discovered by George Ravenscroft in Britain in 1674. George Ravenscroft replaced the calcium typically used in glass manufacture with lead oxide. The resulting glass had a significantly improved appearance and was much easier to manipulate during the manufacturing process. According to standards set by the European Union, glass must contain an excess of 24 percent lead to be considered true crystal, or it must be labelled crystallin or crystal glass.
During its early history, quality lead crystal was highly sought after due to its appealing appearance. However, the discovery of lead's toxicity has decreased lead crystal's popularity in recent times. Lead crystal leaches lead out into food and beverages, especially when they are stored in lead crystal for extended periods of time. For this reason, the use of lead crystal to store or hold foods and beverages is not recommended by health and regulatory agencies.