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Cleaning native copper

Posted by Kyle Eastman  
Cleaning native copper
February 17, 2006 12:09AM
This last summer I collected some excellent native copper specimens from a commercial copper mine called the Teutonic Bore in Western Australia. Some of the pieces are covered in bright green malachite which is quite attractive, however others(in my opinion) would benefit from having the malachite etched off to better display the crystals of the copper. What is the best way to go about doing this?
-Kyle
avatar Re: Cleaning native copper
February 17, 2006 03:39AM
Kyle,

Are you sure it's malachite, or just the green tarnish that forms on copper??

One of the most common (and inexpensive) ways is to go to your local hardware store and buy muriatic acid and soak the pieces in that. However, this method is best used when there are NO crystals present and you don't really care about anything except removing tarnish or if you want to remove any carbonate (calcium, etc...) from the piece. If you are cleaning pieces with crystals, by all means, don't!! You run the risk of damaging the crystal faces and ultimately ruining the asthetic quality of the piece, at least in my opinion. I know you can also use sulfamic acid (coffee pot cleaner) to clean copper, although it is a much slower process it's also a much safer one to the copper; not as likely to etch.

CaptPaul
Re: Cleaning native copper
February 17, 2006 03:39PM
Thanks!
I am fairly sure it is malachite, but not 100%. I have actually tried muriatic acid, and it cleans fairly well, but some sort of coating always seems to return after I take the specimens out of the acid. I will not etch pieces with crystals until I have a reliable techinque to do so. That coffee pot cleaner idea sounds like a good one.
-Kyle
avatar Re: Cleaning native copper
February 17, 2006 05:44PM
    
After you take the specimen out of the acid bath, you do need to neutralise the specimen. Soaking in a baking soda solution will deactivate any remaining acid.
avatar Re: Cleaning native copper
February 17, 2006 08:41PM
Kyle,

What we always did in Michigan after we cleaned our copper was to dip the pieces in something called "Copper Brite", which is a mixture of chromic acid and other chemicals. What this does is put a real thin coating on the specimen to keep it from oxidizing again.

Another trick to clean copper (and silver too) is to dip it in TarnX, which I have found won't etch crystals. If you can't find any of these chemicals, another old trick is to simply rub the crystals with your fingers providing you can do so without cutting yourself winking smiley
Re: Cleaning native copper
February 18, 2006 07:14PM
Many thanks again for all the useful info! I'll see if I can find Copper Bright and TarnX. The crystals seem to be all intergrown, some of them forming branch-like aggregates, which would look nice all shined up. Most of the crystalline specimens are too small to effectively clean with my fingers, and unfortunately most of the larger pieces appear already to have suffered some chemical weathering. I'll see if I can post pictures once I find a reliable cleaning technique. Thanks!
Barry Strieter
Re: Cleaning native copper
February 23, 2008 06:54PM
I found some Copper up in the Upper part of Michigan, I would like to clean it It is with some other type of stone, Can I use mutiatic acid to clen it.
Re: Cleaning native copper
February 24, 2008 04:39AM
Coca Cola removes secondary oxidation products from native copper.

(Removes apatite from teeth too, in case you want to switch to ceramic teeth.)
avatar Re: Cleaning native copper
March 28, 2008 11:35AM
There are a number of ways to clean copper. If the quality of your specimens is high, nice crystals for example, you may want to consider eliminating some of the methods. If your specimens are in the tourist rock range, you can get pretty aggressive in cleaning them. Another consideration would be what minerals are associated with our specimens. Most fine copper specimens you may not want to clean all that much, or not at all. Another factor in cleaning copper is how much you know about chemicals and how to handle them. If you can post a picture of the specimen(s) you want to clean and give some indication of how much you know about chemical reagents, we may be able to advise you better.
Rock
John Kupar
Re: Cleaning native copper
August 10, 2008 06:25PM
We just returned from the UP of Michigan with some great uncleaned copper samples. A few may be half breeds (Copper & Silver). What is the best way to clean these samples?

Best Regards,

John
Re: Cleaning native copper
August 10, 2008 07:05PM
Hi! I've heard about a method using potassium tartrate + NaOH + H2O, but I don't remember the portions now /: I'll write when I find these informations.

Good luck!
John Kupar
Re: Cleaning native copper
August 10, 2008 09:16PM
I look forward to receiving the formula. Have you tried the vinegar/water solution mentioned above? We visited three old mines in the UP of Michigan and found several excellant examples in the tailings. Even found a hand drill from the 1850's!

Thanks!

John
avatar Re: Cleaning native copper
August 10, 2008 10:45PM
John,

Please read my earlier posts (CaptPaul) to get a start on cleaning your UP coppers.

You must have been there for the Mineral Retreat?? What 3 mines did you visit??
Re: Cleaning native copper
August 11, 2008 12:21AM
hi there try ketchup, we us it to clean all or cape d or copper it works great
Re: Cleaning native copper
August 11, 2008 01:16AM
    
Hello,,The trick with cleaning and keeping native copper tarnish free is what you do when you have completed the acid process.
This is what I do and it works well on small pieces but when specimens are large and very dendritic it's just good.
The idea is to get the acid and water off and dry as fast as you can.
1..remove specimen from acid and rinse in water
2..now rinse specimen in a container of warm water thoroughly
3.rinse the specimen in metholated spirits.This enables the remaining water to mix with the metho and when removed to dry does so quickly.
4.lightly coat the specimen with your choice of copper type varnishes
I'm not fond of doing this as most native coppers are best preserved as they are
Costas
avatar Re: Cleaning native copper
December 07, 2008 02:26AM
Kyle

Sorry I didn't see your message earlier.
I don't like to clean any "green" off native copper - whether natural oxidisation or any of the many copper mineral coatings.
However, given your question here are two tips:

(i) I don't think you can get TarnX in Australian but you can use Goddards Silver Dip - you can generally pick this up in the cleaning sections of Coles or Woolies or any hardware store. You could also look at some of the car wheel cleaners - some of these have similar principal chemicals.
(ii) Rather than use a copper varnish you could consider hair spray - much easier to apply and more importantly, to remove.
Cheers
Re: Cleaning native copper
January 11, 2009 08:34AM
    
One method that I experimented with a few years ago seemed to work miracles with corroded copper. It was a variation on the "cyanide bomb" process that the plating industry used all too often, that is until the industry realized just how insanely dangerous the process was and how efficient the legal system was becoming.

The original process involved placing the copper piece to be cleaned into a bath of saturated sodium cyanide solution, adding a slug of 30% hydrogen peroxide to the container in one portion and then running like hell. Within a few seconds, the mixture would flash to steam, ejecting a cloud of boiling hot water, cyanide solution, steam, oxygen and a cloud of deadly hydrogen cyanide gas into the air and all over the immediate surroundings. For the life of me, I cannot imagine a more foolhardy way to clean and polish metal. For somebody to take such a stupid risk, there had to be some sort of payoff at the end.

There was. Not only did the the process instantly remove hard, pitted corrosion, it actually imparted a mirror-bright polish to the workpiece. I can only assume that it did so by first reducing the oxide coating and then removing a layer of copper a few atoms thick. I've seen the results of the cyanide bomb technique and it looked as if somebody had invested several hours of elbow grease instead of a few seconds time (and half a lung).

I had read somewhere that thiourea, the main ingredient in Tarn-X, was finding many new industrial uses, mostly replacing cyanide in some metallurgical processes such as leaching and plating. I had access to a lab and the proper chemicals at the time, so I attempted to duplicate the cyanide bomb process by simply substituting thiourea for sodium cyanide. I was pleased to discover that the experiment worked perfectly on the first attempt. While it was still a violent exothermic reaction and very messy, at least there was no cyanide to clean up. Even so, this reaction is an "outdoors only" experiment.

The process imparted a beautiful mirror shine to several non-ferrous metals that I bombed, even to stainless steel.

Frank
Re: Cleaning native copper
January 11, 2009 11:25AM
HF - Hydrofluoric acid , but be verry, verry careful: Hydrofluoric acid is extemely corrosive and a contact poison.
regards
Anton
andrew
Re: Cleaning native copper
October 13, 2010 08:33AM
clean with hydrocloric, brighten with vin and salt, then coat it immediatly, and dont play with cyanide!! unless ur a nut case like the previous comment
Re: Cleaning native copper
October 13, 2010 12:58PM
    
The problem with cleaning copper is in keeping it clean. Some treatment methods such as with HCl seem to not stay clean as long as others. It seems that some methods activate the surface making them more susceptable to tarnishing. At best all cleaning methods are temporary unless you coat the sample with something afterward ( like lacquer). I haven't tried this, but if the sample has no matrix, heating it and coating it with a thin layer of wax might work better than lacquer and is easier to remove if you need to.
The results also depend on the impurities in the copper, some Michigan copper will not clean at all. The best thing I have found to clean copper (in that it stays cleaner longer afterward) is using citric acid. However even then you can expect it to tarnish brown in a couple years if not sealed with something.
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