Handy tip for you folks, although some may already be at it. Got a nice Irish Georgian rummer recently. Unfortunately there was some unsightly light scratching in the bottom of the bowl due to careless cleaning. So what I've done is find an old champagne cork, and screwed a 3" screw into the bottom to act as a handle. Wrapped this in a bit of masking tape for finger protection, so you now have a mini cork mortar. Popped in a bit of fine cerium paste and rotated the cork round and round the bottom of the glass using a fair bit of downward pressure. Time consuming, but it appears to be working....