When processing glass surfaces, a distinction is made between additives and subtractive processes.

In the additive process, damage to the glass surface is done with resin  filled, hardened and then polished. 

With the subtractive method,  on the other hand, there is minimal removal of the material (glass). The glass surface is minimally removed until an intact glass surface is achieved.

The predetermined breaking point caused by damage  (Scratches) in the glass are thus removed and the homogeneous stress curve, as in the origin of the pane, is restored. 
Finally, the complete and unclouded transparency of the glass surface is achieved by further grinding and polishing.