section_path: Types/Silicate glasses/Lead glass
section_name: Lead glass
paragraph_text: Lead glass
  
  The addition of lead(II) oxide into silicate glass lowers the melting point and viscosity of the melt. The high density of lead glass (silica + lead oxide (PbO) + potassium oxide (K O) + soda (Na O) + zinc oxide (ZnO) + alumina) results in a high electron density, and hence high refractive index, making the look of glassware more brilliant and causing noticeably more specular reflection and increased optical dispersion. Lead glass has a high elasticity, making the glassware more workable and giving rise to a clear "ring" sound when struck. However, lead glass cannot withstand high temperatures well. Lead oxide also facilitates the solubility of other metal oxides and is used in coloured glass. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glass); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb ion renders it highly immobile and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda–lime glass (10 vs 10 Ω⋅cm, DC at 250 °C).