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GeneralCleaning native Copper.

1st Jun 2005 22:40 UTCJohn Steenbergen

Hi there good people,just wondering if you can help with this little problem.I supose it has been asked many times over. I have a lot of Copper laying around both stuff that has gone through the smelter and also large natural specimens of native Copper. Have tried many ways of cleaning this and making it look pretty but to no avail The strongest stuff i tried is the hydrocloric acids this cleans it just beautiful until i take it out then it turns green.I don't really go any stronger then this acid is there something on the market that will take the tarnish and dull copper look off and make it shine? Such a pitty to have these beautiful big specimens sitting here and looking so dull and ugly. Perhaps some of you might know of a simple way to clean these? John

2nd Jun 2005 00:26 UTCAlfredo

Vinegar and a toothbrush is all I use to clean the native copper pseudomorphs after aragonite from Bolivia. I guess it would work equally well on any native copper. Cleans without leaving an unnaturally bright surface.

2nd Jun 2005 08:14 UTCJohn Steenbergen

Okay Alfredo i shall have a go on the solid chunks and see how it goes but what about the wiry stuff? Any idea there? Some of the ones i have are like a birdnest. Thanks for the tip anyway John.

2nd Jun 2005 14:13 UTCAlfredo

For "birds nests", use vinegar followed by an ultrasonic cleaner rather than scrubbing with a toothbrush.



2nd Jun 2005 17:40 UTCChris van Laer


Try neutralizing the effects of acids by soaking them in a solution of common baking soda, then scrub/ultrasonic.

3rd Jun 2005 11:36 UTCRock Currier

If you have the nerve to try something stronger you can try an acid dichromate solution to clean copper. This has been used commercially by various mineral dealers in the past. Take some concentrated sulfuric acid, add about 5% by weight or potassium dichromate or chromic acid and stir till dissolved. This will give a thick dark red/brown solution that will immediately eat up what ever it touches, but it will usually clean copper quite beautifully. This is a very dangerous reagent to use unless you know what you are doing. Use rubber gloves an acid resistant apron, and eye protection. Do not put or pour water into this reagent as it will be converted instantly to steam and blow right back out at you. It will completely eat up a damp paper towel in just a few seconds. The copper is usually very bright and many people think that it is just too bright to look any where near natural. The copper only needs to remain a short time in the reagent and when you take it out you should immediately wash it off in large quantities of cold water. If you want to clean copper half breeds from Michigan I can give you another reagent to clean this material well if you want the silver to be extra bright.


3rd Jun 2005 14:16 UTCDavid Von Bargen

One of the problems with doing this is you really should properly dispose of this cleaning solution (the chromium is what got a lot of plating concerns into trouble with the EPA).

3rd Jun 2005 22:57 UTCJohn Steenbergen

Hi ,thank you all for the tips but this stuff Rock discribes is a no no as it is just not worth the bother and chances are i would spill some knowing me. I think i leave them as they are or dump them. I just thought there was a safe way,a solution of some sort that would do the trick. After having a talk with my good friend from the Brisbane museum,he strongly advised me not to use the strong accids and reckons it could kill a person if spilled on any part of the body. John

4th Jun 2005 15:28 UTCMike

You might not be neutralizing your acid enough after cleaning it. If the hydrocloric is working good for cleaning, just try to neutralize the specimem more after you're done cleaning it.

4th Jun 2005 23:01 UTCJohn Steenbergen

G'day Mike,you got me going again,you say in your letter (you may not be nutralizing ) What do you mean by this? As it comes out of the hydrocloric acid it is beautiful and shiny,but what happens next is i wash the acid of the specimen with plenty of water. And bingo within a matter of time the beautiful specimen turns dull again and starts to go green.So i thought well i'll fix this problem and sprayed it with hairspray. No good! Somebody said stick it in milk which sounded stupid, but ofcourse i tried. Then vinigar,then something else, but all failed.But it is a challence and am having fun. John

5th Jun 2005 04:24 UTCAlan Plante

The rule of thumb is that you need to rinse the specimen in clean running water for three times as long as you soaked it in acid. So for each hour of acid bath you're looking at three hours of rinsing in order to make sure you get all the acid off the specimen.

PS: There is a "Mineral Cleaning & Preperation" forum down the menu a bit. People who do a lot of this sort of stuff tend to read that forum and respond to queries - more so than are likely to pick up on a query placed in this forum.



5th Jun 2005 08:03 UTCJohn Steenbergen

Hey thanks Alan,you know something? I have never ever looked into this part of the forum and did'nt even know this was there. Now i can see that all the answers are there! How dopey can one get.

2nd Jul 2005 19:18 UTCTed French


I use a 50%/50% water and muriatic acid,

It cleans the copper very brightly. Then I neutralize the acid in baking soda. After they dry, I coat them with clear spray paint. After that they will stay bright for many years.

Ted French

3rd Jul 2005 20:05 UTCRob Woodside

Savages!!! You are ruining good coppers sticking them in acids. Fortunately there are a lot of well crystalized copper specimens that aren't wrecked with acid. Your activities merely make these more valuable. I used to think that Michigan silvers were acid eaten, indistinct blobs; until I got an education at the Seaman Museum. There is little more disappointing than to see a harshly etced copper or silver.

27th Feb 2012 20:15 UTCdavid towle

We use a very old method to clean native copper nuggets. All the old collections in Michigan museums were originally cleaned with ketchup. The proccess I use is to put the nuggets in Muriatic acid for ten fifteen minutes to remove any iron, dirt and calcite. then rinse in several pails of clean water and backing soda, so to nuetralize the resido acid. You can air dry them at this point to check them out or you can go to the next step. Take an ice cream pail and empty one or two bottles of any ketchup into the pail. Put the nuggets into the ketchup, making sure they are all covered. Leave them in there for 4,5,6 days. I remove them with a large spoon with the holes in it. Then rinse off the kechup and let them dry off. The copper will look just like the first day they were made. A bright and natural shine. A few may some times oxidize back to a fuzzy green. These will not clean up because of the mix of impurities in the copper. This ketchum method will keep your copper specimens in a like new natural condition for many years. I have some that we cleaned 20 years ago and they still look like they were just cleaned yesterday! If some tarnish and you don't like the look through them back in the ketchup for a few days and they will be back good as new. While the nuggets are in the ketchup, cover the pail so the ketchup doesn't dry out. The ketchup can be reused till it starts turning a brownish black color or you need it for your hambergers. Yuk. The ketchup can be thrown out normally as there is no harmfull or dangerous chemicals used. The muriatic acid can be thrown out following the instructions on the bottle. I like to nutrallize it with baking soda before getting rid of it. Also we don't use vinigar as it can etch the copper. Making a valuable specimen worthless. So enjoy the ketchup cleaning proccess, it works. Dave

8th Oct 2013 01:32 UTCDan the 2nd

I am new at this but...

I have several large copper nuggets, the biggest 30 lbs and the smallest 5.5 lbs

One of the pieces is copper and quartz. (sort of like a pokey birds nest)

I used muriatic acid on all of them (I did not dilute the acid), some came out quite nice, and just needed some buffing. Others came out all black and red. Sat in the acid for 5 hours, and then out and into baking soda and water for 15 hours.

I am having trouble getting the shine and luster and I cant figure it out.

I've tried vinegar and salt (short period of time)

and I also used tarnex (brushing on) after the wash in water, copper looks dull again.

I am starting to think, the only way to get proper shine is with a wire brush. (Which is tough labor and time consuming)

I have done lots of research, but I have not found a clear cut answer.

Anybody who can help or give advice, I would greatly appreciate it.

8th Oct 2013 01:36 UTCReiner Mielke Expert

Copper that has a lot of arsenic in it cannot be cleaned with chemicals. This is not all that uncommon with Michigan copper, and is probably what you have.

8th Oct 2013 02:28 UTCPaul Brandes Manager

Unfortunately Dan, leaving your copper in muriatic for 5 hours probably damaged it beyond repair now. Usually, one never leaves copper in muriatic (if it is even used at all) for no more than maybe 5 minutes to strip off carbonates IF there are no crystals visible. If one suspects any crystals then much milder methods must be used. Some other options include vinegar (again watch the time it is in) and yes, even ketchup.

8th Oct 2013 14:05 UTCDan the 2nd

Wow 5 mins only in the acid, I will have to note that, thank you.

How long? In ketchup? Or salt and Vinegar?

I do have a crystalline sample. (it came out black from being in the acid after long while, I checked on it almost every 15 mins, with little noticeable change to its surface.

Any guidance is appreciated.

I think i only had one piece actually get ruined from the acid, because it etched the metal to the point where you could see what it was made of, lighter and darker pieces of copper.

again thanks for the help in advance, this has certainly been a learning process.

8th Oct 2013 14:21 UTCDan the 2nd

I want to add a note most of my copper pieces, were covered in oxidation and red and black, before I even put them in the acid. This wasn't simply a nugget with just oxidation, lots of hardened dirt and debris.

Some of the pieces retained crevices that had large chucks of green oxidation even after being in the acid.

8th Oct 2013 14:35 UTCDan the 2nd

Okay more questions. As mentioned before, I am a newbie and have a great deal of learning to do.

For the future:

1. Should I take a wire brush to it first, cleaning dirt and debris and surface oxidation. (skip if fairly clean already???)

2. Then 5 minutes in acid (muriatic acid)?

after that's complete,

3. I let it soak in baking soda and water for 15 mins? (3 times longer than acid soak)

4. Then theoretically, I am ready for clear coating? (right?)
Note: this has never been the case for me, usually I have to retouch it up with wire brush

thank you for your time - Dan

8th Oct 2013 14:42 UTCDavid Von Bargen Manager

"Should I take a wire brush to it first," - A wire brush could scratch the copper. If you have any decent crystals on the specimen, you will ruin the value. Hosing it off is better (also pressure washing if you have the equipment)

8th Oct 2013 15:24 UTCKeith A. Peregrine

I use a dish scrubber to remove as much dirt as possible after letting the rock soak in water for a while. There are some with very stiff bristles and others with soft. I use both depending if there are any visible crystals present, copper or otherwise. Stiff ones are good for softening and removing tough grime, but they can damage crystals or soft material. In that case soft bristles are preferred.

As for cleaning copper, what I've encountered is when using dilute muriatic acid, the copper will quickly tarnish from collected from most Keweenaw dumps, a few don't. I've always attributed this to impurities within the copper though I have never tested that thought. The copper generally tarnishes to a dull brown or red brown color, sometimes almost black. A soaking in white vinegar usually brightens it up, but as it dries it dulls again. I have found that the quicker you dry the copper, the more of a shine is retained. Even then I've not succeeded very well in keeping a good shine. Copper Bright is supposed to coat copper to preserve the shine, but I've only used the liquid version, didn't work. Supposed to use the powder Copper Bright. Hope to obtain some soon when I visit the UP again this weekend.

Curiously, freshly cut copper seems to retain its shine easily, which makes me think that there has been some reaction with muriatic acid and vinegar. I've discovered that thin to wire copper can thus be etched or even dissolved in muriatic acid. Seeing that others have made this observation earlier, I need to experiment with other acids in removing calcite in the hope of not damaging the copper or other desirable minerals present. I can't say for sure, but I'm getting the impression that muriatic acid removes the luster of Prehnite, leaving it dull. Some Microcline color appears washed out, though I can't be certain that it happened during crystallization.

8th Oct 2013 16:34 UTCDavid Von Bargen Manager

A lot of the UP locals use sulfamic acid to clean copper. Seems to be a lot gentler than muriatic. It is available in UP rockshops.

8th Oct 2013 17:20 UTCRonnie Van Dommelen Expert

I agree with Rob that etching in HCl can ruin nice copper specimens. I tend not to clean mine at all, though the recipe below makes me want to try it...

In the March-April 1972 MinRec, Yedlin on Micromounting column, he describes a recipe to avoid the etching. You need a 'non-porous vessel', 1 part lye (sodium hydroxide), three parts Rochelle salts (potassium sodium tartrate), and twenty parts distilled water. Suspend the copper, by a copper wire and dowel, from the top of the container. Shortly the liquid will turn blue. Lift the specimen a few times to check on it. When ready, rinse. Take proper safety precautions with the lye.

I have not tried the recipe or know of anyone who has, so I can't comment further. I would love to hear if someone does try it.

8th Oct 2013 17:20 UTCDan the 2nd


I use a wire brush, attached to a power drill, seems to have softer bristles.(does not scratch too much) Does a good job, and keeps the shine long enough for clear coating. However, if you have a crystalline / pokey bird nest shape, its hard to get to the interior edges.

I think your right about the U.P. copper, some of it shines great, but others are stubborn and return to dull color, time and time again, Wire brush, seems to fix this. but its ALOT of work. and makes it hard to get into nooks and crannies.

8th Oct 2013 18:54 UTCMickey Marks

Place the copper in a bathtub and fill with hot water. Take a sponge and some soap and scrub the copper until clean. But first, do not forget to remove his uniform and badge.

8th Oct 2013 23:21 UTCScott Sadlocha

I have been using a watergun on some of my copper, but it is a laborious process that usually takes multiple sessions. Personally, I HATE what HCl does to copper. I learned this the hard way, soaking a nice Phoenix Mine copper in dilute HCl for just a little while. All defined crystal edges were damaged, and the piece had that typical "burnt" look common to acid soaked copper, and some of the faces were hackly. After spending time looking at many copper pieces now, I can usually quite easily see a piece that has been acid soaked.

Everyone is different, but my preference is a natural looking piece, patina and all. To me, bright, shiny copper is unnatural and that is not how I want my pieces to look. I am still looking for a good method to clean. I am heading up to the UP in a couple days, and I am going to stop in to some of the shops of there to grab some sulfamic to try it on a couple representative pieces. I have found vinegar to work decently, but again it restores shine. If I have a piece that I absolutely don't want to lose the patina, I have found mechanical cleaning the only means (watergun and picks, soft brushes, etc.)

9th Oct 2013 01:31 UTCDan The 2nd

Hello again,

I have a 10 lbs quartz and copper piece, it took the acid bath, and now is black.

I have removed most of the black with the wire brush, but there is still a lot I cant get to.

How do I get rid of the rest of the black removed? (Hi powered water washer?) or is it hopeless?

Help me out if you can, I am looking to clear coat soon.

thank you

9th Oct 2013 04:40 UTCRob Woodside Manager

Clear coating will just add to the damage of an acid eaten copper, but it could make a lovely decorator piece. The decorator market is nowhere near as fussy as the specimen market.

9th Oct 2013 13:57 UTCDan the 2nd


I hear you, but are you saying a blackened, specimen with 0 cleaning will sell better?(I would tend to largely disagree)

(check out ebay and look at non cleaned versus a dirty and oxidized)

Also rob, seems that my piece was not damaged by the acid, because of the black coating.

I wish I could show you my before and afters. Visually my pieces took 20 steps up and kept most of its natural look, just with a little extra shine.

also if you don't clear coat, your going to loose most of the shine. I want people to walk in and say wow, whats that.

9th Oct 2013 14:03 UTCDan the 2nd

I am re-posting my question,

Hello again,

I have a 10 lbs quartz and copper piece, it took the acid bath, and now is black.

I have removed most of the black with the wire brush, but there is still a lot I cant get to.

How do I get rid of the rest of the black removed? (Hi powered water washer?) or is it hopeless?

Help me out if you can, I am looking to clear coat soon.

thank you

9th Oct 2013 15:03 UTCKeith A. Peregrine


In cases where the copper turns black, I place it in white vinegar. Usually this removes the black, but in many cases it turns dark again, though not black. One way to minimize this is to place the copper under a heat lamp. The longer water stays in contact with the copper, the greater the dark tarnish. Rarely do I want to have a bright copper, just want to expose it.

The reason I use muriatic acid is to dissolve (etch) the calcite. In many cases I have no idea what lies beneath the calcite. This past Copper Country Retreat I ended up with a great piece containing flecks of silver and copper on top of gemmy epidote. Since there was a lot of calcite, I let it sit in the dilute muriatic acid foe over an hour. None of the copper was crystalline, simply flakes. However, I shall bite the bullet and use another acid to etch away the calcite in the future. If my impatience can handle it....

9th Oct 2013 20:04 UTCRob Woodside Manager

Dan, the specimen market pays kilobucks for good xls, but nothing for an acid blackened piece, no matter how shiny or coated it is. The specimen market is brutal on nice untreated Cu specimens with no xls. (Copper skulls excluded) The is also a strong monetary bias for specimens with a mine locality.

27th Mar 2016 06:46 UTCPeterMac

I too have some nice pieces given to me from a Queensland mine. All of the suggestions have relied on acids of one form or other; from very strong chromic, sulfuric, hydrochloric (Muric), acetic (vinegar), mild citric (tomato). The stronger the acid, the more oxidizing, which can result on black copper oxides. The green is residual chlorides from salt, tap water or hydrochloric acids. Significant carbonates can cause blue or green staining, but the conditions are very specific.

A mild acid, free of chlorides, over a longer time is preferred after the "dirt" or gange is removed.

I use to use Coke, which is about 3 percent phosphoric acid, low in chlorides. Rinse, and leave immersed in water for7 days before exposing to air. If you want to keep just for visual purposes. Give a light spray of Mr Sheen, a mixture of non oxidizing light oils to reduce later oxidation. (I been told different cokes now have different formulations... So you may have to experiment)

27th Mar 2016 12:43 UTCKeith A. Peregrine

With added input from friends and previous results, I have now gone over to Sulfamic acid. Reason being, Muriatic acid will etch some copper. While taking considerably longer, Sulfamic does not attack the copper. The acid is used to remove calcite which generally covers areas of interest such as vugs. Acid is also useful in quick cleaning, that is not much more than a dip, rinse, scrub, and soaking in water.

One technique I am using and still experimenting with, is using compressed air to blow off water on a specimen, then placing the specimen under a heat lamp for ten minutes or so to evaporate off any remaining moisture. This has given me good results in preserving the 'bright' luster of copper.

As Rob points out, if you know you have copper crystals, do not use any acid bath!
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