Lead glass

Lead glass, also known as lead crystal, is a type of glass that has lead in it. Normal glass has calcium oxide in it, while lead glass changes the calcium oxide with lead(II) oxide. It looks nice because the lead is very large and heavy and changes how the glass looks. Lead glass rings when tapped while ordinary glass does not. This glass can absorb some X-rays. It is very insulating. 
It contains between 18 to 40% of lead (II) oxide by weight. Any glass that contains at least 24% PbO by weight is referred to as “lead crystal”. Any glass that contains less than 24% PbO by weight is referred to as "crystal glass". Lead glass has a chemical composition of silicon and lead oxides, with other elements added to get colours or properties.
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. The presence and quantity of PbO are what determines some of lead glass’ most important optical and physical properties.
Applications of lead glass.
The properties of lead glass make it useful for many applications. Here are a few examples: