Defining Terms: What Distinguishes Crystal from Glass?
Strictly speaking, crystal is a type of glass.
Unlike plain glass, crystal contains lead. When lead is added to glass it gives the glass more weight, increases its resilience, and adds a brilliant sparkle. The addition of lead oxide to glass also makes it easier for blowers to manipulate without reheating and makes the material better suited for molds, leading to more dynamic designs. Full lead crystal can only be labeled as such if it contains at least 24 percent lead oxide.
Due to concern that the lead in crystal could cause health problems, many manufactures are now promoting non-lead crystal. Both types of crystal are made with sand, soda ash, and limestone with barium oxide in place of lead.
Both lead and barium give the glass an extra brilliance and clarity not found in plain glass. Though it can look similar, lead crystal is the only true crystal while non-lead crystal is a brilliant form of glass.