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Blackening when plating indium over silver

We have a requirement to plate indium over silver, diffuse, then black oxide. We are getting "blackening" of the high current density areas of the diffused indium-silver when black oxided. Even happens when all baths are new. Any ideas?

Patricia Mihalik
aircraft engines - Indianapolis, Indiana
1998

I have seen silver become almost a metal sponge in high current density areas at a cd too high for the formulation. I suspect that you are absorbing blackening agents into this area more than the rest of the plate.
An interference color shift from the surface roughness or texture may only be apparent after it is darkened.

James Watts
- Navarre, Florida
1998

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