Rod,

We use Ammonium Sulfate.  It works very quickly, and it can identify partial
removal of the chromate as well.  It works under the same principle as the
other tests where the clean copper turns black/blue from oxidation, whereas
the uncleaned areas stay the bright copper color.  It stinks real bad, but it
is very accurate.

Scott Griggs
Senior Applications Engineer
RBP Chemical Corp.
(612) 825-6113

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