Originally Posted by BavarianFanatic
I don't think using a claybar on glass is a very good idea. Glass isn't as hard and abrasion resistant as paint. For one, it's not intended to do anything for scratches. If anything, it'll CREATE them. It's sole purpose is to remove contaminants that are on the surface. It's also a first step prior to polishing for the sole purpose of removing contaminants in an effort to avoid grinding them into the paint as you polish. The damage caused by the clay is polished away. This isn't quite as easy with glass. There's a very high potential for doing more harm than good with clay unless you really know what you're doing.
A claybar is fine on glass with proper lubrication. Detailers use it all the time to remove water spots. I get great results with it all the time. Its very easy and anyone can do it.
Glass is much harder than paint. Hence why paint polish won't correct glass and the need for Cerium Oxide.