This was a pretty deep scratch. This is an outside window, accessible via a landing (many floors up).
This is tempered glass, with no coating on the outside.
There were multiple scratches, and each was circled.
Focusing on this scratch, I started the sanding – and you can see the progression as the scratch disappears.
Also notice, the deeper I sand, the larger the area that is sanded. This process is called feathering, and is necessary to avoid any perception of optical distortion.
This image below is a bit more of a closeup of the initial sanding:
Almost finished with the sanding. Notice how the sanding area around the scratch is getting larger.
And then, the final initial first stage sanding:
With the depth of this scratch, it required a much larger surrounding area to be sanded.
Next, the the pre-polish sanding was completed. After the surface was completely prepped, the polishing stage cleared up the glass to a brand new clarity.