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I have a couple of small wooden boxes with metal inlay that I would like to restore.

The wood was originally black and the metal silver in colour, but the black has faded and the metal has corroded.

So, can anyone help me with how to:

  1. Remove the copper oxide without further damaging the wood?

  2. Stain the wood black again without staining the metal?

Is it as simple as rubbing the metal with something acidic, restaining the wood and then polishing the stain off the metal?

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    Welcome to Arts & Crafts. You've got a challenging project. Can you clarify a couple of things? The question refers to the metal as silver in one place and copper in another. Also, the filigree loops in the wood look like they might be embedded metal wire. Is that the case? Can you tell what kind? Does the sheetmetal work have any kind of protective finish? Is the wood just stained or does it have a protective finish? re: your question at the end -- unfortunately, it won't be that simple. Best case, it will be a complicated, meticulous process. Worst case, after that it will be a mess. – fixer1234 Jan 11 at 19:28
  • Thanks @fixer1234, so I don't know what the metal is. Its silver coloured, which is what I meant in my post, but the colour of the corrosion suggests copper so I guess its probably an alloy. – James Jan 12 at 14:28
  • Could the copper color be some type of finish or anodizing or does it appear to be the actual surface of the metal? A couple of clarifications are critical to any advice on restoration: 1. Does either the metal or wood have any kind of protective finish (either clear or something providing the color), or are we looking at bare wood and metal? The wood looks like it has a few shiny spots, and the metal color looks like it might be a finish of some kind. 2. Are the filigree loops in the wood embedded metal wire or are they some type of surface decoration? – fixer1234 Jan 12 at 20:13
  • I'm not sure but I think: 1) The wood has no protective finish other than the stain/dye used to colour it. The shiny areas you note are the areas where the black colour is strongest. I have no idea how the colour was achieved. 2) The metal has no protective finish that I can see. 3) The green isn't anodizing or a finish because I've had the boxes for years (they've been in the loft) and the metal started off all silver coloured. Pretty sure its the metal oxidising. 4) I'm not sure if wire is the correct term but the filigree is definitely actual metal that's been hammered into the wood. – James Jan 12 at 20:45
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Let me start with a disclaimer. If it was my box, I wouldn't try to restore it. There's a good chance of turning it into a mess. Right now, it shows the character of age. Trying to restore it could leave you with something very unattractive.

The wood seems bare, but if it had any kind of sealer (possibly including the stain), you will end up with a blotchy finish if you don't sand it first. It would be tough to sand it without damaging the sheet metal, which looks like it isn't removable without damaging it.

If the sheet metal has any kind of protective finish, the results will be blotchy. If it has a copper patina, it's likely solid copper sheet. If there are irregular small blotches of dark patina that aren't consistent with natural sources like finger prints, that would suggest that there might be a protective finish (or it could have been something in contact with the metal at those spots). The proper way to restore it would be to first strip any potential finish or coating, but it isn't very practical to do that without removing the metal. So you will be taking a chance with any kind of cleaning.

There's a potential for creating a mess on the wood from what you do on the metal, and on the metal from what you do on the wood. It's risky to do this kind of stuff after the fact.

So I would advise against trying to restore it, but I'll provide some tips and ideas on doing it if you're set on doing it.

  • Remove parts that can be easily removed without damage so you can access the surface of the box unobstructed and work on the removed parts without messing up the box.

  • Do meticulous masking. Seal off the metal when you work on the wood, and the wood when you work on the metal. Regular painters tape isn't good enough. I would put down an edge strip of something like rubber cement to seal the surface, then something like FrogTape, which blocks water-based materials from getting past the edge.

  • If the filigree had been a surface decoration, you'd be out of luck. Since it's the edge of embedded metal, it theoretically would allow you to re-stain the wood. But it won't be as simple as slapping on some stain and wiping it off. The stain will soil the metal, and cleaning it off the metal will mess up the stain on the surrounding wood.

    You can try to apply stain and wipe it off while it's still wet, and see how cleanly it comes off the metal. You may need to employ a procedure like using a penetrating stain, letting it soak in deeply and dry, then lightly sanding the surface with extremely fine grit sandpaper. You could also try using a tiny brush to apply the stain around the filigree, being careful to avoid the metal (a very slow process).

  • Cleaning copper isn't the problem. The problem is keeping it that way. Copper starts to oxidize as soon as you stop cleaning it. Cleaning dissolves the oxidation, and leaves a microscopically rough surface with a lot more surface area. So every time you clean it, it oxidizes faster. And every time you clean it, you remove some of the copper.

  • Many weak acids will remove copper oxidation. Lemon juice, orange juice, or vinegar are popular. People use tomato sauce or ketchup (the tomatoes are a little acidic; ketchup also contains a little vinegar). Commercial cleaners often use citric acid. For heavy oxidation, people add salt, or use a baking soda paste as a mild abrasive. You can mix the acid with a little flour to make a paste that you can apply and let it sit for awhile. There's an interesting comparison of the effectiveness of various popular mixtures: Compare Home Made Copper Cleaners.

    Commercial products may clean copper faster, but that's not necessarily a good thing. They do it by using stronger, more aggressive acid, which will lead to a need to re-clean sooner. Some also contain a chemical used to purposely create patina. I'm guessing that's in there to create the need to use the product more often.

  • If you don't protect the metal, it probably doesn't make sense to clean it. You can coat it with oil (which will also be good for the wood), so you can do the whole box. If you use a permanent finish, it will need to be something impervious to air and moisture. If any air or moisture gets through, the copper will oxidize under the finish, and the finish will make it all that much more difficult to clean it again.

  • You don't necessarily need to restore everything to it's original appearance. You can do things to merely improve how it looks now. For example, touch up the most worn areas of the wood to be consistent with the rest, or restore only the aspect that bothers you the most or is the least risky. It may improve things just to clean the box.

    Sometimes, it's sufficient to just make things more uniform. For example, the wood has some dark blotches. Rather than staining all the wood, you may be able to lighten the blotches.

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Thought it would be useful to show what I did and the results. So, in the end I:

  1. Cleaned the metal corrosion off using vinegar. Initially with a cotton bud but then I switched to gently rubbing using a scouring pad. I checked the vinegar didn't affect the wood/stain first on a small patch underneath first.

enter image description here enter image description here

  1. Oiled the box with mineral oil.

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I was pretty happy with the results, apart from the discolouration you can see in the top left of front of the lid. I tried to stain it with black boot polish, which is what I suspect was used in the first place, but it didn't do much. I might try again with something else at some point.

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  • Hi James, is the discolouration visible on the front side of the wooden top of the box? I'm not completely sure if that's what you're referring to. In any case, it looks great! – Joachim Feb 2 at 18:43
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    Hi @Joachim, yes the top left of the front of the box. Its the edge of the lid itself – James Feb 2 at 18:53

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