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How To

Setup and operating instructions for Wndsn distance tools and related items.


Patina on Brass, Copper, and Bronze Tools

Brass is an alloy of copper and zinc while Bronze is an alloy of copper and tin and other metals like nickel or zinc.[1] All of these will naturally tarnish when exposed to oxygen, even more so when touched with bare hands, in the process developing a thin, dark, mostly uneven patina pretty fast.

Tarnish?

Tarnish is a thin layer of corrosion that forms over copper, brass, silver, aluminum, magnesium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, gray or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals and protects the underlying layers from reacting.

Tarnish actually preserves the underlying metal in outdoor use, and in this form is called patina. Patina is the name given to tarnish on copper based metals.[2]

Tarnish is a product of a chemical reaction between a metal and a nonmetal compound, especially oxygen and sulfur dioxide. It is usually a metal oxide, the product of oxidation. Sometimes it is a metal sulfide. The metal oxide sometimes reacts with water to make the hydroxide; and carbon dioxide to make the carbonate.

Thus, to force a tarnish, expose the metal to an agent containing sulfur to speed up the reaction.

Verdigris

The green patina that forms naturally when copper, brass, or bronze is weathered and exposed to air or seawater over a period of time usually consisting of varying mixtures of copper chlorides, sulfides, sulfates and carbonates is sometimes called verdigris.

It is usually a basic copper carbonate, but near the sea will be a basic copper chloride.[3]

Natural patinas in copper

Copper goes through a natural oxidation process that forms a unique protective patina on the metal. The surface of the metal undergoes a series of color changes: from iridescent/salmon pinks to oranges and reds interspersed with brassy yellows, blues, greens and purples. As the oxide thickens, these colors are replaced by russet and chocolate browns, dull slate grays or blacks, and finally to a light-green or blue-green.[4]

Regular cleaning and maintenance (if you want to prevent or remove tarnish)

After every use: A microfiber cloth dipped in hot soapy water removes dirt and dust buildup. A toothbrush can help clean out holes and engravings. After wiping down the metal with a soapy cloth, rinse the item and dry it thoroughly.

Weekly: Wiping the tools with a little liquid ammonia (a solution of ammonium hydroxide) on a soft cloth will help keep the surfaces shiny. The metals look brighter and require less polishing if rubbed with a cloth moistened with olive oil after each cleaning. The olive oil retards tarnish.

Polishing

To polish, you can use special commercial polish or anything lightly acidic - lemon, vinegar, or even tomato juice work well. Clean with soap and water afterwards. Again, not polishing will protect the metal by keeping the tarnish as a barrier to further corrosion and wear.

Heavy stains and corrosion

To remove heavy or uneven tarnish:

  • Wash in hot, soapy water
  • or a weak ammonia and water solution.
  • Dip a slice of fresh lemon into table salt,
  • or make a paste of flour, salt and vinegar.

Rub into and over the corroded area and thoroughly rinse with water afterwards.

Forcing patina

Wndsn: Partially masking and aging brass

To selectively force patina:

  • To remove oils and contaminants before applying masks or suspending in fumes, clean the surfaces with citric acid.
  • To only have specific areas affected, mask what should stay raw with electrical tape or decals to create surface designs.
  • Expose or suspend in vinegar or ammonia fumes.[5][6][7]

See also:

References:

  1. Wikipedia: Copper and copper alloys 
  2. Wikipedia: Tarnish 
  3. Wikipedia: Verdigris 
  4. Wikipedia: Natural patinas in copper 
  5. Wikihow: Patina on brass 
  6. Wornandwound: Forced patina on bronze watches 
  7. Patina science