A car we did a few years back had very bad scratches on the inside of the windscreens, caused by a succession of women using the back of their left hand to 'demist' the screen. The diamonds in their rings gouged the glass.We took both screens out, laid them on the lawn, and used 'Brasso', a mildly abrasive brass cleaner on them.
It worked, but it took a lot of elbow grease.
johnboy