Those copper class A soda-acid fire extinguishers hung in school hallways across the county through the 1950s and 1960s. They have been turned into lamps, tables and decorative accent pieces and today, they have become collectibles. Most of the time, they have a fine green patina resulting from years of oxidation and neglect. The paint might have worn off of their face, perhaps from being touched by generations of school children. Cleaning them up is a simple exercise in kitchen chemistry.
Mix 2 cups of white vinegar with 1 cup of table salt. Stir the mix to form a thin paste of about the same consistency as thin gravy.
Apply the paste to the copper surface with a paint brush. Use long strokes, applied lengthwise on the body of the extinguisher. In the tight areas around the top and bottom of the cylinder, daub the paste on thickly with the brush. Allow the fire extinguisher to stand for 15 minutes.
Use a clean rag to scrub the surface, lightly. As you scrub, you'll see the metal begin to return to its copper color as dirt and tarnish are removed.
Rinse the copper surface with clean water. If you do not rinse the surface, it will tarnish in a matter of hours.
Air dry the copper surface. Do not dry the surface in direct sunlight; this will cause the copper to change colors. If you notice a white powder on the copper surface, rinse and dry again.