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Thread: Cleaning very badly tarnished copper

  1. #1
    Brintiff is offline Amateur Metal Finisher
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    Default Cleaning very badly tarnished copper

    I picked up a really cool old fire extinguisher, it's made out of copper with brass plates on it. I'd like it to have it looking like a mirror. It is the most tarnished piece of copper I have ever seen, it looks totally black.

    At first I thought it may have been painted but after looking it over it looks like it is just tarnished. Is anyone aware of what I could use to soak the whole piece in to get a good start in removing the tarnish? I could start using my Foredom and felt bobs but that will take forever and I really don't want to use my buffer until it's time for a final polish.

    I'm not looking for a store bought copper cleaner meant to hand polish small pieces. Any type of acid that will eat the tarnish and not the copper? Even if it will eat the copper I'm willing to use it, I'll just have to keep an eye on it.

    I'm aware of the issues with cleaning and polishing antiques, this will be going in my den so I am not concerned with any perceived loss of value.

  2. #2
    mpierich is offline Metal Finishing Guru
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    Default Re: Cleaning very badly tarnished copper

    Was a fellow in here claimed muriatic acid worked - get it at a builder's supply (maybe pool supply too). Use at own risk.

    Me, I'd just go to town on it with 400 grit or so, but that's me.

    Also look through Caswell's goods here, they might have something.

  3. #3
    Rasper is offline Metal Finishing Guru
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    Default Re: Cleaning very badly tarnished copper

    I bought a table lamp for 5 dollars at a yard sale once. It was heavy and shaped beautifully, but the finish looked like dark brown paint. I figured it was painted steel. When I peeked under the paint, it wasn't paint at all, but 70 years of tarnish on brass. I went at it with tripoli and it came right up. Then I finished it with red rouge. Gorgeous.

    R

  4. #4
    woodjames's Avatar
    woodjames is offline Metal Finishing Guru
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    Default Re: Cleaning very badly tarnished copper

    Brintiff,
    Aluminum Brightener (Caswell's) works well on copper, it won't etch the copper at all, but will remove oxidation, albeit slowly. Mix at .5 gallon to 4 gallons of water. Hydrochloric acid (Muriatic) works well but MUST! be diluted. You want a 10% concentration (referred to as pickel 1), it'll take off the oxidation also, but it's a fumer, so wear a mask, add acid to water. Keep this one away from the vicinity of steel and chrome items as it'll rust steel and eat chrome on nearby items at full strength. It will etch it left in for a while, but mainly just activates. Use a grout sponge to help things along in either scenario.

    -Jimmy


    Quote Originally Posted by Brintiff View Post
    I picked up a really cool old fire extinguisher, it's made out of copper with brass plates on it. I'd like it to have it looking like a mirror. It is the most tarnished piece of copper I have ever seen, it looks totally black.

    At first I thought it may have been painted but after looking it over it looks like it is just tarnished. Is anyone aware of what I could use to soak the whole piece in to get a good start in removing the tarnish? I could start using my Foredom and felt bobs but that will take forever and I really don't want to use my buffer until it's time for a final polish.

    I'm not looking for a store bought copper cleaner meant to hand polish small pieces. Any type of acid that will eat the tarnish and not the copper? Even if it will eat the copper I'm willing to use it, I'll just have to keep an eye on it.

    I'm aware of the issues with cleaning and polishing antiques, this will be going in my den so I am not concerned with any perceived loss of value.
    James Bateman

  5. #5
    Brintiff is offline Amateur Metal Finisher
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    Default Re: Cleaning very badly tarnished copper

    Thanks guys, I tried using brown compoundicon, takes way too long, even the black doesn't remove it fast, it's some tough stuff.

  6. #6
    Rasper is offline Metal Finishing Guru
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    Default Re: Cleaning very badly tarnished copper

    Okay, then here is the big gunicon. Sulfuric acid. That will take it off.

    I use it regularly on copper sculpture pieces in preparation for chemical patinas. Dilute it first with distilled water. Distilled because you don't want any unknown minerals in the mix from tap water. (Battery acid is sulfuric acid; I am not sure how dilute it is; maybe straight from the bottle would be perfect.)

    Be careful. Sulfuric acid is not to be taken lightly. Never pour water into acid; always pour acid into water. Always wear eye protection.

    R

  7. #7
    Gurthang is offline New User
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    Default Re: Cleaning very badly tarnished copper

    Using an acid will do the trick but work carefully otherwise too long exposure can result in a porous / pitted surface.

    Pete

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