plating, anodizing, & finishing Q&As since 1989
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
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 compounds. This causes copper and/or silver sulfides and sulfates to form. The result in either metal is a darkening. The products used for this purpose are generally called flour of sulfur, Liver of Sulphur [affil link] 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 flour or liver of Sulfur with water is a Sulfuric Acid solution! Caution is called for!
- Frederic, MI, U.S.A.
No, Dale, you will not create sulphuric 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
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