Glass repair

Yesterday at our local Tesco's Autoglass were doing free chip repairs. So off i went with the Focus to have one repaired, and then went back a short time later to have two of them done on the Mondeo. While i was there i asked the bloke if there were any trade secrets on how to remove scratches from glass, as i have a scratch on the drivers door window about 3 inches long. He said there was this stuff called "Jewelers Rouge(sp?)" which is like a very fine rubbing compound. Apparently its very hard work but should polish the scratch right out. He didnt know where would sell it and ive never heard of it before, so i was wondering if anybody on here had any ideas?