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How to know if a part has been processed with black oxide or black zinc

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Hi,

Our local plating supplier has sent us a part that he says is black zinc. We did a small test submerging in salty water for 3 days and in some parts the black came off. I suspect that the part has black oxide instead of black zinc, is there a test (chemical) that we can use to be sure of this?

Thank you,

Alejandro Jiron
Consumer - Cartago, Costa Rica

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Dear Alenjandro Jiron

Its easy to check the parts with zincblack Just dip a part in Con.Hcl, U will get vigorous gassing(or Stripping) if it is zinc black.

Shetty
- Bangalore, India

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Dear,

Oxide coating are remove in dilute cyanide solution while zinc black do not.

GULSHAN SACHDEV
- MORADABAD U.P. INDIA

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