What Causes Copper to Tarnish?

Copper Garden Items

• Despite the cost, copper garden ornaments are worth the investment because copper handles exposure to sun and water well. Some copper roofs have lasted centuries and the Statue of Liberty, which gets its famous green color from the verdigris on its copper exterior, is still standing in the corrosive environment of the Atlantic Ocean. Manufacturers commonly use copper in home plumbing both indoors and outdoors with the expectation that it will not fail. Copper's durability makes for long-lasting and beautiful birdbaths and fountains. Flat copper strips, placed in the garden, will deter slugs.

Copper

• Copper is a soft metallic element represented by the symbol Cu. This element is a good conductor of electricity and is most commonly used in electrical wires and circuits. In addition, copper conducts heat well, leading to its use in pots and pans. Because copper corrodes in the presence of acids to produce toxic byproducts, do not use pure copper pots for cooking acidic dishes such as tomato sauces. Copper cladding on the bottom of the pan is perfectly safe. You can recycle copper and some people recover copper from old houses and electrical wires.

Copper Tarnish

• Tarnish is not the same as rust, although the initial formation goes through a similar process. Rust is corrosion caused by the oxygenation of iron. The rusting of an item will continue until the metal has completely flaked and disintegrated. Tarnish, or patina, self-limits the corrosion. As soon as a fine coating of tarnish forms on the surface, it protects the underlying metal from further corrosion. The patina found on copper occurs because, in the presence of moisture, the oxygen and carbon dioxide in the air combine with the copper to create a mixture of copper (II) hydroxide -- Cu(OH)2 -- and copper carbonate -- CuCO3. These compounds create an interesting green color often used as a pigment. Additionally, in the presence of mild acids, this process can be speeded up to create a 'faux' patina, although patinas created this way are not self-limiting and do not protect the copper below the surface because the molecules are not as interwoven and they flake off revealing the copper beneath.

Cleaning Copper

• To remove copper tarnish from pots, birdbaths and decorations, use a combination of vinegar or lemon juice and salt. Make a paste from the lemon juice and salt and apply it with a toothbrush. Some experts, such as those at The Penny Collector, also recommend using toothpaste but this is not as effective as a mild acid and salt. Do not leave the acid and salt on the copper items for long and rinse the copper items thoroughly. To prevent further tarnishing of the copper, coat the copper with a clear acrylic coating. For small items, you can use clear nail polish.