Arrested for blackening metals with cyanide

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

• Cyanide is used to blacken brass in the Flemish process. Cyanide makes the finish both blacker and more easy to relieve.
• It is used in bluing steel. In this case it is mixed with caustic soda [affil link] and arsenic. I don't know whether producing receipts for purchase of arsenic would help exonerate him or only land him in deeper trouble :-)

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.

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!

Regards,