Goldsmithing Use of Cyanide

Greetings! This is my first time to post a question to all of you - please excuse any breach of etiquette! Does anyone have any detailed references or procedures for how cyanide was used in goldsmithing - either currently or historically? My limited information says it was involved in the cleaning/polishing(?) phase. Is this true, and if so how specifically? Thank you in advance fir your responses! Paul Smith

Cyanide is used in “bombing” to give gold pieces a thin layer of pure gold. Any older jewelry text would detail the process…IDK if it is used that much anymore or not, as I don’t work in gold. Basically you put the jewelry into a solution of potassium cyanide and then pour in some peroxide and this leads to an effusion of cyanide gas and a boilover, hence the name bombing. The process actually removes some gold and leaves a clean, pure gold layer. This should be done under a fume hood or outside, as cyanide gas is released. -royjohn


Thank you for taking the time to reply to my question. That was very helpful! Thanks, Paul

We’ve used it in a similar fashion to what Roy said, but with putting the cyanide in a beaker, and hooking it up to our plating rectifier (iirc, with the anode and cathode reversed compared to normal plating). This essentially ‘electro-strips’ the piece. We really only do that when something went wrong in casting or during a torch operation that left oxidation in an impossible to reach area.
We have the need to do it maaaaybe once a year, if even that, but it’s super handy when it’s needed.

I have and still use cyanide. Mostly for plating purposes. Most gold and silver plating solutions are made of cyanide with the gold or silver “salts” suspended in them. It is also used for electro striping and cleaning. Sadly it is also still used for extracting gold from ore. Cyanide process | metallurgy | Britannica
So is mercury. Toby Pomeroy is doing his best to help eradicate polluting and dangerous methods of gold mining.
I have used it in the past for Bombing as well. If you want a detailed description of bombing I can provide that in another post.
Cyanide is relatively safe to use if you don’t drink ingest it. Still wearing gloves and working in a well ventilated area is always a good idea.

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I have powder potassium cyanide at work that I use for cleaning. Heavily diluted into water. I mostly use it with chains to clean and remove oxidation. Couple of seconds in the solution and move around with my copper tongs and then a lot of rinsing under water. Gold chains come out looking brand new and don’t have to go though all the bother of trying to polish chains on the machine.

Thank you for the very informative reply! If I could impose further, I would appreciate any detailed procedures for ‘bombing’ as I’d like to try it myself. I already have the cyanide and can assure you that safety will be foremost - I’m a degreed chemist and microbiologist. I work with gold and primarily do a lot of casting and think this method could be useful. Any references or pointers are always appreciated - as well as your time to be so helpful! Have a good week! Paul Smith dba The GoldSlinger.

Paul Smith

I “bombed” extensively in the early 80’s. Raw castings, both gold and silver. used Murray Bovin’s “Jewelry Making” technique, One ounce of sodium cyanide, 1 oz of 30% hydrogen peroxide in one quart of 200 degree water. Dissolve the cyanide in the water, add the jewelry and then add the hydrogen peroxide, Murray said to cover the container and agitate. I always found the chemical reaction much to violent to hold and agitate. I usually added the peroxide and walked away about 6 feet.
A couple of cautions, be sure the water temp is hot enough, in cooler water the chemical reaction is very sudden, I remember the solution blowing 10 feet in the air in cooler water. The peroxide you use on cuts is 3%, you need 30%.
I was told years after the chemical reaction totally breaks down the cyanide into inert ingredients, I am not sure if it is true.
Castings that had just had the investment blown off came out bright and shiny, very often the sprues were removed and the jewelry was sold as a finished product. The number one advantage is that all fire scale was removed from 925 silver castings.
I did try electro-stripping at one point, a large, heavy duty Vigor plating unit with a cyanide bath with almost the same results. It turned out to be more work and I did not like the idea of a permanent cyanide bath sitting around.
Funny, I was on another forum maybe 10 years ago and someone was complaining about the “orange peel” on silver castings. I responded “that is fire scale, just bomb the jewelry”. Almost immediately there were at least 7 responses telling me that was dangerous!
I remember a professional finisher on the top floor of the jewelers building in Boston. He did all his bombing in a laundry sink in front of a window with a 20 inch window fan. We used to joke about the dead pigeons on the roof! (we had no idea, it was only a joke)

You might want to know that any acidic solution will convert cyanide salts (KCN & NaCN) into HCN gas…which was at one time used in the gas chambers for executions.
" A hydrogen cyanide concentration of 100–200 [ppm] in breathing air will kill a human within 10 to 60 minutes." If you smell almonds you are in trouble
Hydrogen cyanide - Wikipedia.

Careful, careful, careful!!

Yes! Yes! The danger cannot be minimized!

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I believe in the early experimentations by Stanley Lechtzin with precious metal electroforming, he used some sort of cyanide to accomplish the task. In the 1970’s, I did a little testing with non-cyanide electroforming liquids. You really must know your “stuff” with this chemical or, bye bye!