Here is the reason why I asked the question...I had a Model 39-2 and the finish on the frame was pretty chipped and scratched, my gunsmith cooked it in his ultrasonic/hydrosonic cleaner with the heat on, it lifted most of the anodization off the frame, he then polished off the rest, with the result being a pretty trick looking two-tone 39-2. I just picked up a 6904 with a frame in the same condition, so he tried the same process - and after 3 days of cooking the finish has not budged. This is why I was wondering if the process was different between the two pistols. Now he is thinking he will have to glass bead the frame on the 6904 before polishing.