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[disambiguation needed]. When food is in lead glass, lead might come out of the glass and into the food. Acidic foods such as lemons leach lead much more easily.