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Name: David A. B.
Status: Other
Age: 40s
Location: N/A
Country: N/A
Date: September 2002

Is there a substance or process which can be applied to copper flashing and roofing caps to turn them green? in a dry climate of the western United States, the copper turns dark rather than green.

There are commercial products available to promote the formation of "patina" on copper. Do a search on for "copper patina" and you will find several sources.

Vince Calder


Although I do not know the precise answer that you are looking for, I understand your problem.

Copper and bronze are oxidized outdoors by acidified precipitation. The acidity of the precipitation that you do get is not nearly as great as it is in the eastern United States. Therefore you don't get the same oxidizing effect. I can imagine that a very diluted acid, perhaps Muriatic acid would accomplish the job. But I would check with a local commercial builder who uses copper roofing materials in construction to see what they say. Any acids, dilute or not must be handled with the appropriate personal protective equipment - face shield or goggles, long rubber gloves, etc.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory

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