I discovered this by chance.  I often boil stained fabric in oxyclean so I had a canner full of the solution waiting for it to cool.  I had just purchased a badly discolored glass lampshade and had tried soap and water to no avail.  It was quite ugly, so I decided to drop it into the oxyclean and it cleaned up beautifully.  I have since used it to clean up some frosted chimneys that were also discolored.  DO NOT ever put any aluminum products into oxyclean, however as it will turn them black.