Copper flashing on range hoods or house exteriors can be cleaned easily without scrubbing, using a flour paste with vinegar and salt. Here are simple steps for removing oxidation from copper flashing.
Mix up a batch of paste cleaner for copper. Put one cup of flour in a large bowl or small plastic bucket. Add one teaspoon of salt and mix with the flour.
Add about six ounces of white vinegar to the flour mix to form a thick paste, stirring as you add the vinegar. Use double proportions for a larger batch, or half proportions for a small job.
Apply a thin coat of the paste to the copper flashing using a brush or small trowel. Leave the paste on the surface for 5 to 15 minutes.
Remove the paste with a damp sponge, or with a hose if you are working outdoors. Rinse the flashing with mild detergent and water to remove any residues, and wipe dry with a clean, soft cloth.
Apply a coat of clear spray lacquer to keep the copper color bright longer.