Thermal reflow of glass and fused silica body

A process for making glass plate comprising the following steps:

• (I) providing a ready-to-flow notched glass tube having (a) a longitudinal tube center axis, (b) an identified section between two cross-sections perpendicular to the tube center axis having a longitudinal section length L1;
• and (c) a notch in the direction of the tube center axis of the ready-to-flow notched glass tube through the tube wall;
• and
• (II) thermally reflowing the ready-to-flow notched glass tube thus formed in step (I) at an elevated temperature to form a glass having a refractive index variation of less than or equal to 10 ppm, wherein the step of thermal reflowing comprises:
• (IIa) placing the ready-to-flow notched glass-tube on an essentially horizontal longitudinal mandrel, with the mandrel inserting into the inner cavity of the tube, and the notch placed facing sideways;
• (IIb) allowing the lower part of the notched glass tube to roll out to an essentially vertical position while restricting the upper part from rolling out, to result in a partially rolled out glass piece;
• (IIc) placing the partially rolled out glass piece on an inclined surface;
• and
• (IId) allowing imposing an external force on the mandrel to mechanically assist the partially rolled out glass piece to roll-out on the inclined surface to form an essentially flat glass plate.