The main difference between Glass and Crystal lies in the presence of lesd oxide.
This oxide gives glass certain Characteristics that make it particularly interesting.

Pbo, in fact, increases the dendity of glass and consequently greatly increases its refraction index. This kind of glass thus approaches the optical properties of diamomds: the light that touches it is refracted much more than normal glass thus giving it that particular brillance typical of lead crystal.

The greater the content of lead oxide, the greater is his effect.
Only glass that contains at least 24% lead oxide can be legally called CRYSTAL or Crystal glass.
A higher content of lead oxide, however, would give a yellowish colour to the glass.

Only with the close collaboration between specialised chemist and master glassblowers can the composition turn into a clear, trasparent, brillant and stable material, worthy of being called CRYSTAL.