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Arrested for blackening metals with cyanide


Q. I'm a French chemist, and I'm trying to defend an innocent man who is in jail, because he has bought one kilogram of cyanide. The French expert does not believe what he says: that he has bought cyanide to blacken iron. Could you give me some literature and references about the subject to help this man. This man was a metalographer but he could not prove that it is possible to blacken iron with cyanide. Help him by sending me everything interesting on the subject, and especially, references to the literature.

Robert S [last name deleted for privacy by Editor]
- France


A. Per the "bible of the industry", the Metal Finishing Guidebook and Directory --

Per Metal Colouring by D. Fishlock, a black electroplating process for iron, called The Gray Arsenic finish uses sodium cyanide and copper cyanide.

The use of cyanide in metal finishing is pervasive: from cleaning, to oxidizing, to blackening, to plating, to slowing or accelerating other processes. Some finishes including silver plating are virtually impossible without cyanide. There has to be more to this case than you've told us here, because no real expert could possibly fail to acknowledge the pervasive use of, and countless applications for, cyanide in metal finishing.

Further, people do not have to be correct before they buy a chemical with an intention to use it for metal finishing. So even if your client cannot demonstrate successful bluing or blackening of iron is little evidence that he did not buy it for this purpose.

But I hope the readers who encourage plating at home are reading your example of one more thing that can go wrong on them.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


Q. What are the reactants and reaction in "bluing" iron? Was this process ever involved with using Naval Jelly [affil link]?

Larry B [last name deleted for privacy by Editor]
- New Orleans, Louisiana

May 28, 2008

A. Hi, Larry. Naval jelly is a phosphoric acid based rust remover / rust converter, used to convert "red rust" to "black rust" -- so it could be involved in bluing somehow, but it can be involved in other things too; likewise, bluing can be done without involving naval jelly at all. Hot, strong caustic, with some form of nitrite oxidizing agent is used to put "black oxide" or "blueing" on steel.

Questions that are cast in the abstract can almost never be answered well, even after a dozen "ifs, ands & buts", so most readers don't try. Instead, please tell us what is going on, i.e., what is your own situation that motivates this question, and then you'll probably get some good answers. Thanks!


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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