I just love your purple rags in a bag and I’ve turned many of my friends “on to them”, as well. Recently my husband and I purchased a pellet stove. Somehow in the process of figuring out how to run it, we managed to get the glass covered with a lot of streaks. They looked like that gunky grease that turns brown on your oven window.
Anyway, we were sure that we would have to buy the glass cleaner from the dealer. But, purple rags to the rescue (!) it took a little elbow grease but I got it all off with just plain water. My husband said “those things are just great, aren’t they?”