"Matty F" wrote in message
...

Cerium oxide is not something I've come across: how did you come to be
working with that?

I use it to polish windows. I can polish out the scratches caused by a
missing windscreen wiper, and some of the scratches caused by morons
who use sandpaper near the edges of the windows of heritage vehicles.
It's not easy - it could take half an hour to polish a small area
using an electric drill with a leather pad. And then that area could
heat up and crack.

You can buy it from telescope manufacturing suppliers.
I have used it in the past to polish mirrors after grinding them with
carborundum (sp?) grit in grades from 60 to 1000+.
The pitch lap with a nylon shirt on it works wonders for polishing mirrors,
knocks hours off.