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world gathers for metal finishing
Q&As since 1989


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Accelerating copper corrosion

How can copper pipe, for a dry interior decorative location, be treated to accelerate corrosion? Not looking for verdigris finish, just the nice dark brown that exposed copper gets before going to green.

Dan D [last name deleted for privacy by Editor]
- Hanover, New Hampshire
2002

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By far the easiest and safest way to tone a copper or bronze object is to bake it in an oven at 350 or so Fahrenheit. This will stimulate an oxidation reaction in either metal and darken it somewhat. Getting the item to darken evenly may be a challenge.

The second technique for darkening these metals, and by far the most common, is application of sulfur [affil links] compounds. This causes copper and/or silver sulfides and sulphates to form. The result in either metal is a darkening. The products used for this purpose are generally called flower of sulfur, or liver of sulfur [on eBay or Amazon] or something of the sort. Many of the commercial preparations prepared for darkening or toning metals are also sulfur compounds. Unless I am mistaken, the result of mixing flowers of, or liver of Sulfur with water is a Sulfuric Acid solution! Caution is called for!

Dale H [last name deleted for privacy by Editor]
- Frederic, MI, U.S.A.
2002

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No, Dale, you will not create sulfuric acid that way, but liver of sulfide can release a lot of sulfur dioxide into the air (which is why it acts like and smells like rotten eggs), especially if acidified.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007