Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical glass. In past decades, it was a popular material used to create decorative vases and bowls as well as crystal glasses and decanters. Lead glass is also known as X-ray glass or radiation shielding glass as one of its major applications is in the absorbance of high energy radiation while maintaining optical transparency. Also, lead glass has a lower thermal conductivity than lead-free glass. Interestingly, even though stained glass windows are a type of leaded glass, industry experts often use them separately to create distinction between the two.