Crystal glass: Old, refined but by no means crystalline
When you buy a glass from crystal glass, you normally know that you are purchasing a high-quality product. This was already known in Venice in the 15th century, and crystal-clear glass could be produced there.
Per definition, crystal glass is a colourless glass with metal oxides normally mixed into. However, the term is rather misleading because it is derived from rock crystal.
The glass, however, is by no means crystalline but amorphous, that is, a substance where its atoms are not arranged in a clear structure. A true crystal is exactly the opposite: the arrangement of the atoms shows a very clear structure here.
By the way, there is a legal definition as to what the glass must contain to deserve the name crystal glass. In addition to the glass matter itself, the substances include potassium oxide, lead oxide, zinc oxide or barium oxide. The law also stipulates the exact quantitative proportions.
By the way: Do you know "Bohemian crystal glass"? Well, this glass does not contain metal oxide but chalk, that is limestone. As you can see, hazardous ingredients are not a must.