Blackening brass problem - Metal Work, Soldering and Metal

I've run into a problem blackening some brass parts. I've done it hundreds of times before without a problem. Sand or file the pieces, pickle in vinegar for an hour and rinse. Soak in Acetone for an hour and rinse. Put in 1:5 dilute Blacken-It for an hour. There is a reaction, but the result is a

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