Originally Posted by jrajpaul
I've clayed the glass and tried using BMW glass polish with poor results. The problem is definitely the glass and not the wipers. I suspect it needs a machine polish.
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.
The BMW glass polish (or any other consumer product) isn't intended to remove scratches. It's really only a cleaner. You can take care of very light scratches and haze with products like Bon Ami and Bar Keeper's Friend which are very mild cleansers. Anything deep enough to catch a fingernail will require more aggressive abrasives such as cerium oxide. But beware, you can quickly do far more harm than good if you're not experienced doing this. Glass isn't nearly as forgiving as paint.