About Lead-free Crystal
From the Illustrated Glass Dictionary at GlassOnLine.com:
The type of glass produced when lime in the batch is replaced by lead oxide. The composition of lead crystal is 54-65% silicon dioxide (SiO2), 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2O), and other oxides. Such glass has a high refractive index and is particularly suited for decoration by cutting.
Barium oxide derived from BaCO3 (witherite) is used principally in optical and crystal glass instead of lime or red lead. Glass which contains barium is lighter than lead crystal but gives comparable brilliance due to its high refractive index.