I'm interested to see if anyone has any insight into the hard crystalline green corrosion (?) that you often see in watches. It seems particularly prevalent on rotors, see below on the watch I recently did. From the quick search I did I am reasonably sure it is brass corrosion product, can anyone confirm? But very interested if anyone has a good way to remove it other than using abrasives? I tried rust remover but didn't seem to do anything, and also put it in the ultrasonic with