On Friday, March 3, 2017 at 1:21:14 PM UTC-5, N_Cook wrote:

All this is one the external sections of the pins? how would these
effects progress into the active die or at least weld-spots ?
This piece of kit was not stored i na damp environment, so no chance of
capilliary action.

This is all happening at the chemical level by electrolysis. So the corrosion would follow the path as the copper starts being exposed. Clearly the silver-over-copper extends into the body of the die - and the same oxides would form within. Once the process is established, no moisture is really necessary, just oxygen and time. You have to understand that the galvanic action is made much worse by the presence of silver making copper act as a sacrificial electrode to the silver reacting with anything attacking it and whatever the base metal might be.

The thickness of the coating - at least several molecules - is plenty wide enough, if you will excuse the expression.

Peter Wieck
Melrose Park, PA