Has anyone ever seen a black residue left on stainless steel passivated parts? We have some small clips that were said to be passivated, but were very dull and had a black residue when you rubbed the parts. This is the vendor's test house response:
 
 To determine if the part had been passivated it was submerged in a copper sulfate solution (4g CuSO4, 10ml H2SO4, 90ml H2O) for 3 minutes. This is a standard test to check for passivation. The absents of a copper deposit on the part indicated it had been passivated. 

Comments:  The copper sulfate test indicated the part had been passivated. The rougher than normal surface condition could have given the appearance of surface contamination under some lighting conditions.

Partly confused because everything I read says passivation cleans and shines part.

 

 

 
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