Chemically polishing or electropolishing silver: cyanide peroxide "bombing"

"The Electrolytic
and Chemical Polishing
of Metals in
Research and Industry"
by W.J. Tegart

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A. Hi Kimball -- that's a tough one. A friend of mine who is a process engineer with a jewelry company asked the same question in Metal Finishing magazine, and we couldn't come up with great answers. However, one reader offered the following opinions:

"By far, the most effective chemical polish is the "peroxide-cyanide bomb", but due to the volatility of hydrogen peroxide you need to make additions, or a fresh solution continuously. Plus you have to deal with cyanide in the effluent, and possibly with cyanide released to the atmosphere."

(When someone calls it a "bomb", I also worry about its stability -- I've seen it done under a lab hood but I couldn't see much).

Not as good in his opinion, but worth mentioning, were a fluoboric acid/boric acid mixture that is supposedly available in a proprietary formulation from Patclin Chemical Co., or cathodic treatment in a sulfuric acid/ferrous sulphate ⇦this on eBay or Amazon [affil links] bath.

Good luck!

Ed. note: Ed. note: Accu-Labs, Inc. [a finishing.com supporting advertiser] now carries the Patclin Chemical line.

Hagerty Silver Polish

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A. Kimball

The electroless cleaning technique that Tyler suggests is a good one. You can also use household ammonia ⇦this on eBay or Amazon [affil links] as the electrolyte. A problem is that these techniques micro-roughen the surface making them sensitive to recontamination. After cleaning the silver surfaces should by polished with a cleaning compound that contains an anti-tarnish agent.

A. Dear Sir:

I have been in the jewelry manufacturing business for 22 years. Bombing, as it sounds is a very serious operation and can be deadly in the hands of a novice. I suggest that you consider ion exchange to clean polished silver articles. I do know the process of bombing and it involves sodium cyanide in a one ounce per quart saturation (heated). You combine this with hydrogen peroxide (30%) ⇦ this on eBay or Amazon [affil links] and agitate. This process should only be done in a glove box because of the explosive nature of the process and the large quantities of hydrogen cyanide gas that is liberated. Hydrogen cyanide gas is the same gas that is used in the gas chamber for execution. Get the picture? There is a method that is much slower and uses the chemicals virtually cold but the result is variable. May I suggest that you invest in the Santa Fe Symposium books [on AbeBooks, eBay, or Amazon affil links] that a company named Rio Grande sells in Albuquerque, NM. There is also a company named Op-Amp tech books that sells this type of information.

The ion-exchange method that I suggest for polished silver is done by boiling water in a clean aluminum pot. Add a liberal amount of baking soda [in bulk on eBay or Amazon [affil links] . Place you silver items in the pot so that they make contact with the aluminum. This sets up an electrical reaction whereby the oxides and sulfides that appear on your silver as tarnish go into the solution and off of your silver. This process works quite quickly, it is safe, there are no disposal problems, and can be done on a hot plate. Leave cyanide bombing to the foolish people.

There is another method of electropolishing gold and silver with a solution of (no free cyanide). This process uses a combination of Thiourea ⇦this on eBay or Amazon [affil links] , Phosphoric acid and a stabilizer (sucrose, or karo syrup). In this process, an electric current is passed through the silver castings while submerged in solution. The anodes and cathodes in this process are made of titanium and can be quite expensive. The whole process must be agitated and it is a cold operation. The company that I did research for using this process was called Technics, in Irvine, CA. I don't know if they still exist or not. The man that I worked with on this project with that company was named Gwynne Edson. I don't know his current status either. Try using a search on the net for electropolish AND Thiourea and see what you get.

A. I am not sure I understand exactly what you are after, but I know if you immerse silver in buttermilk and put it where it can set for several days, then rinse off with water, the silver will be clean without using any polish, etc.

I learned this because I wanted to buy a real silver tea set and it was quite tarnished and I did not know how to clean it. The lady who shared this with me guaranteed it to work, but it must be pure buttermilk.

A. Regarding the "ion-exchange method" for polishing silver, if you don't have an aluminum pot (since most of us use stainless silver these days), you can crumple foil into the boiling water and it works just as well. This method is great for cleaning silver plate, as well as sterling silver.

Ed. note: We have several threads on the aluminum foil method for cleaning silver, including:
Thread 1178u, "Remove silver tarnish with aluminum foil"
Thread 4785, "Polishing Silver with Aluminum Foil and Washing Soda" and
Thread 20650, "How Does This Homemade Silver Cleaner Work?"

A. Regarding electropolishing of silver that Tyler Teague referred to above. This process was patented by me in 1986 and is used on silver/gold and brass with minor modifications. It is marketed through a distributor network in the US.

It is used at a mild temperature (90-100 degrees) @ 2 to 6 volts. Process time for an individual piece may be as short as one minute depending of amount of oxidation in the casting process. Bulk processing in a rotating barrel may take us to 5-10 minutes. This is a Thiourea ⇦this on eBay or Amazon [affil links] process and contains no cyanide.

A. Hi, Gopi. Mr. Edson developed the formulation and then patented it; others cannot copy it without licensing it :-)

I'm not sure if the patent is expired or not, but you can view the patent, and do a search to find its status and some info about the formulation. Sorry, but we can't print the formulation on this page. Good luck.

Regards,

A. Hi. I'm the owner of my company. I have some experience regarding gold polish and silver polish. First you have to bind your jewelry with copper wires then dip the jewelry in boric acid and phosphorus solution; make sure that the solution is quite hot so that it can quickly refine your jewelry. Then plate a thin layer of copper by use of electroplating process, then plate a layer of silver by same method. It will gave a quite shiny look on your jewelry; then plate it with gold. Thanks a lot

A. Hi, Joe. Sorry, I don't know if that network is active these many years later. Please try googling it yourself, using Gwynne's name, the patent number, or other search terms. I don't want to spoil the discussion, but please remember that these public technical discussions, and the opportunity for camaraderie & enjoyment which the forum presents are possible only through the courtesy of our supporting advertisers ... who might justifiably drop that support if their money is spent steering the traffic towards their competitors who don't :-)

Regards,

A. Hi Darryl. We appended your question to an existing thread which we believe answers it. But please get back to us if questions remain.

Regards,

A. Dear sir,
As per my knowledge you first check the purity of your silver metal. Addition of alloy percent may affect scaling. If your silver is pure than you add 92.5% silver and 7.5% alloy. Control under nitrogen /argon gas and melting temperature while casting.

A. To whom it may assist,

I'm a banker with quite the addiction to shiny things and all things silver and gold alike, so imagine the size of my triceps and exceptional lateral arm movements because polishing.

If anyone finds their way back to this artifact of a thread, concerning the polishing of precious metals: depending on the size of the piece you're working with, the best method and ironically the oldest mentioned here, is one coined pickling. The anhydrous acid (compound?) I use is called Sparex ⇦this on eBay or Amazon [affil links] , sodium hydrogen sulphate. It prevents oxidation and removes tarnish in, and I use this word literally, seconds. HOWEVER, the process does require one to anneal the metal prior to quenching in the acid bath. I would only be able to use silver and gold coins when referencing the temperature, and that's roughly 400-650 °F for silver and ~900 °F for gold. Typically, I eyeball it and go with a solid "dull-red" glow. I use a torch. Ah, the mixture for the acid bath is approximately (1) glasses of water PER (1) scoops of powder.

I recommend only this method for silver and gold of all purities, for it is the easiest, cheapest, least complicated and even time may attest to it's convenience.

Highly recommend over buying anything titanium.