The well-mixed batch of about 250 g glass
was melted in a platinum crucible in an electric furnace at 1600 ◦C for 2 h in air.
The glass melt was poured onto a pre-heated iron mould. It was annealed at 600 ◦C
for 4 h to remove the internal stresses of the glass and then slowly cooled down to
room temperature.The as-prepared glass block was cut into desired dimensions
and optically polished for ceramization and to performing different measurements.