Hi Mike,

Have you tried to grind into the nodules to look for a nucleus?  I once had
nodules related to tin flakes (from racks).  The tin flakes were extremely
small but we were able to carefully grind into one and had in scanned at tin.
 Turned out that our platers were not stripping racks as thoroughly as they
should and small flakes were re-depositing on surfaces and on the edges of
holes.

Just a thought, if you exhaust other avenues.

Good luck

Mark Mazzoli

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