Having been looking for a A&F seafarer for some time, I finally came across a ref 2443 1st execution this week. I really like these earlier references for having some of the most beautiful tide indicator sub-dials.

I was wondering what causes a brownish hue to develop on the surface of these dials; it seems to be quite a common phenomenon amongst the A&F seafarers. Furthermore the brownish hue seems to relent at the 3'oclock area. From a more trained eye what does the "white stain" look like to you?