Known for its rich red-brown color when a lantern or sculpture is made, or a roof is installed, copper changes color to various shades of green, blue, brown, and pink. This color change, known as patina, develops when the oxygen in the air interacts with the metal. Patina is so valued that metalworkers and artists simulate the process to turn out pieces that appear aged. Copper is a living metal that only becomes more beautiful over time. When you install exterior copper lighting on your home, you can expect that the metal will age with dignity and add to the overall appeal of your home.

How Patina Develops In Nature

In the presence of heat and water, copper develops patina at varying speeds due to chemical reactions that take place. When the metal reacts to oxygen in the air, carbon dioxide results. As the carbon dioxide reacts with additional oxygen, oxides form that determine the color of the patina. Depending on the amount of carbon dioxide, water, sulphur, and other chemicals that are present in the air, the finish might be:

1. Red to pink, due to the abundance of iron
2. Dark green to blue, due to the abundance of malachite
3. Blue to purple, due to the abundance of azurite
4. Dark green to emerald, due to the abundance of brochantite
5. Black, due to the abundance of sulphur

Greens, blues, and purples are the usual colors of patina, which also develop different patterns as the result of the chemical reaction. The color that forms is due, in part, to the impurities in the copper such iron, nickel, cobalt and molybdenum which all react to other agents of change:

1. Heat can help patina form more quickly, a reflection that the chemical reactions behind the process are happening at an increased rate. Room ventilation and the present of heat sources such as furnaces, stoves, and fireplaces can promote patina on copper pieces within the home, while warmer climates impact copper inside and out.
2. Moisture from rain, snow, mist, and other moisture in the air also advances the rate of patina development. When there is high humidity, where the air is packed with moisture, or a combination of high humidity and elevated temperatures, patina will occur more quickly than in dryer areas. Areas that have lots of rain or snow that drenches copper roofing, lighting, and sculptures are have fast patina development. Inside the home, steam from kettles, pressure cookers, and other appliances can facilitate patina growth.
3. Air pollution from cars and industry also accelerate the patina formation. When the sulphur in air interacts with oxygen, the resulting sulphur oxide interacts with water in the air to form brochanite, which turns copper green.
4. Salt in the air, especially on the coast near oceans, encourages patina to develop in five to seven years as compared to 10 to 15 years in areas with low percentages of salt in the air. In some arid regions, patina may never form.

Patina Development In Action

Naturally weathered copper changes colors the more it is exposed to the elements in the air as it ages, and turns red bronze and eventually blue, green, or turquoise. One obvious example of how the factors of heat, moisture, and air pollution interact with copper over time is the Statute of Liberty.

This 151-foot copper statue positioned in New York Harbor in 1886 welcomes visitors and immigrants with a green covering produced by constant exposure to moisture and salt. Originally a rich red-brown, the statue turned green within 30 years. The Army, which managed the status at the time, proposed painting it to return the color to its original copper, but an outcry from the public and from experts stopped the effort.

While the copper reacted with the elements to produce its trademark color, the iron framework that supports the statue corroded due to these same elements. Reconstruction and repair efforts in the early 1980s were careful to keep the patina intact. Architects, structural engineers, metallurgists, researchers, and contractors diligently worked to keep the finish intact despite considerable structural work. Where the finish was disturbed by repairs, a spray of greenish corroded copper particles similar to the statue’s exterior color were sprayed over region once sealed with coal tar paint.

Changing the Course Of Patina Development

If you love the original rich color of copper, how can you prevent patina? Unless you seal the color with products designed to prevent tarnish and discoloration on brass and copper, nature will take its course. While impractical for a large surface like a roof, you can apply it to copper gutters, cupolas, sundial, lanterns, and other outdoor features. Other products are available to prevent tarnishing indoors.

For small surfaces indoors, you can scrub off patina with a green Scrotchbrite pad and buff the them several times a year to return them to their natural brightness. If you want to encourage patina, you can do via methods such as soaking items in white vinegar, spraying them with salt water and exposing them to ammonia fumes, applying Miracle Gro fertilizer, and more. (A little internet searching will give you detailed information on how to use these methods.) Once you get the patina to the color you want, you should seal it to prevent discoloration.

Loving The Color Of Copper Exterior Lighting

In installing fixtures or major features such as roofs and gutters, you should think of how they will look with your siding color. Once the patina has started, you should consider the color it is at the beginning and the color ii is likely to become in choosing paint or siding colors.

For copper exterior lighting, its changing appearance is what adds character to your home. While the lighting develops beautiful hues, it will not rust or deteriorate like other metals, even in extreme weather conditions. The patina serves as natural protector of the metal, which makes the lanterns maintenance free.

When you are considering new outdoor lighting, Lantern & Scroll offers reproduction lighting in 100% copper in styles designed for any home. To see our collections, visit our website or stop by our Charlotte store.