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How to speed copper oxidation?

  1. Nov 20, 2017 #1
    I'm working on some decorative items made of copper. I'd like to have them achieve the brown color of an old copper penny (or the old copper pipes in my home). I've read you can do this with some chemicals, but due to size/shape I'd like to do this some other way. I'm also concerned that any sort of chemical that I would apply would not give an even appearance.

    I could bake these in an oven - will that help? What temperature? Would adding moisture help? Or does this just take months/years? I would wash them with detergent first to remove any oils, and scrub with an abrasive pad to expose an even, 'fresh' copper surface.
     
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  3. Nov 20, 2017 #2

    Nidum

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    Google : ' patination solutions ' and ' patination treatments '
     
  4. Nov 20, 2017 #3
    Yes, I have. Most are geared towards the green patina and chemical solutions. I just want the 'natural' brown of an old penny, and would like to avoid applying a chemical solution, due to size/shape and getting an even finish.

    I might be able to get them in a (relatively) air tight compartment. Would flooding with oxygen speed things up (days?) I can get oxygen cylinders at a hardware store. $10 for 1.4 oz.

    https://www.homedepot.com/p/Bernzomatic-1-4-oz-Oxygen-Gas-Cylinder-304179/202044702
     
  5. Nov 20, 2017 #4

    tech99

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    If you heat copper in a flame, it immediately develops an oxide coating, which gradually gets thicker, and as it does so the colour changes. The colour seems to depend on the thickness of the coating relative to the wavelength of light, and also whether CuO or CuO2 are present perhaps.. Maybe you can try an experiment? Maybe very gentle heat over a few hours would work.
     
  6. Nov 20, 2017 #5
    If course you must have come across this
    https://www.wikihow.com/Darken-Copper

    maybe try a bag that can be tied shut for a closed environment.
    add some ammonia and put the piece in it hanging from a cord so that only the fumes act on the piece, and not the liquid

    Experiment first with something not valuable.
     
  7. Nov 22, 2017 #6
    Yes I did see that, but ammonia is for the green/blue patina, I'm looking for an old penny oxidized brown look. And yes, they also show various sulfur compounds for that, but I am concerned with getting an even appearance, and chemicals generally seem to leave blotches and drip marks. That's why I'm looking at options for exposure to air or heat.

    I did try baking some scrap in the oven @ ~ 400F for ~ 1/2 hour. It turned kind of yellow.
     
  8. Nov 22, 2017 #7

    TeethWhitener

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    Heating in air should work, but I doubt 400F (200C) is hot enough. Try the cleaning cycle of an oven, which is closer to 1000F (~550C). Or alternately, throw it into a fire.
     
  9. Nov 25, 2017 #8

    Baluncore

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    I believe the final brown colour is not an oxide but an acetate that develops later on the initial oxide layer. Try lightly oxidising the copper and then boiling the copper in vinegar or exposing it to acetic acid fumes.
    Boiling iron in wine will protect it from rusting.
     
  10. Nov 25, 2017 #9
    OK, thanks - I will try that later, and report back.
     
  11. Nov 25, 2017 #10

    Baluncore

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    https://www.wikihow.com/Darken-Copper
    Simple and safe, summary of method 3.
    Step 5. Turns copper a darker brown, roughly the color of an American penny. Mix concentrated hot baking soda. Step 6. Spray the copper with the solution. Step 7. Keep in a humid area for one to eight hours. This patina may take a few hours to develop, but keeping it in moist air will speed this process. Step 8. Depending on the environment and handling, the patina may wear off or fade before it sets permanently. If so reapply.
     
  12. Nov 25, 2017 #11
    leave it in coca-cola!







    i am only kidding.
     
  13. Nov 26, 2017 #12
    NaOH I put a copper wire into Drano solution and it turned brown,
    The same wiki that I quoted.
    Don't know where I messed up with ammonia, as that is for a green color .

    Baking soda did not work for me, It seemed to make the lustre a bit of a shiny mat, with a very slight hint of pink, hardly noticeable.
     
  14. Nov 26, 2017 #13
    I did get a chance to experiment with the baking soda, and like @256bits , I didn't get much of a reaction.

    Will also try the Drano later. Gonna be busy for the next few days. Will report back.
     
  15. Jan 1, 2018 #14
    go to your local gun store they sell browning solutions -also can be found at hobby lobby-! caution ! ammonia has a low odor threshold- also give pickle juice a try.
     
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