With reading a recent thread, one of the replies was to warn away from a movement with some discoloration. I am wondering, what is the main cause? I would think rust, but this is on a particular movement I just acquired - no signs of rust anywhere.
Gallet EP40 movement, I'd say early 1940's. Notice the non-incabloc balance jewel
Contrast this with a slightly later EP40 movement (from my Fathers decimal watch). This would be mid-late 1940's.
Should I be concerned about the new arrival? It is in my watchmaker's hands now. I'm determined to get this one going properly.