Good to hear it smoke! Don't let the clay grab. If it does you need more lubricant. It's real hard to do any damage with clay (I've heard a rumor that it's possible, but can't imagine) but since your car is black, don't take chances. When the clay gets dirty (obvious, just look at it) fold it over and squish it on the windshield to flatten it out and keep going. You don't have to and shouldn't press hard, just let it glide with a little pressure. You can do the baggie test, before and after. (take the weed out first) Take a sandwich bag, put your hand in it and gently rub the surface. Feel the moon under your fingers? Thats what the clay will remove. Do it again after claying a section and notice the difference. If you still feel some bumps, go over it again with the clay until it feels clean with the baggie test. Good luck and get an A on this assignment or you will have to suffer the wrath of this forum.