Mixed raw material called batch is put into platinum pot and controlled temperature and processing time. The melting conditions depend on the glass type. The batch is melted into amorphous glass.
Melted amorphous glass stirred from back side for homogeneity.
After casting, the glass is cooled and crushed. Then the refractive indices are measured for process control. The crushed glass is called "Cullet"
Above picture is cullet. The cullet is melted again in more precise way for consistent optical properties.