All you ever wanted to know about copper

Why and how does copper change color?

Copper has excellent atmospheric corrosion resistance. It becomes naturally covered with an oxide film, changing its color to dark brown/black in normal atmospheric conditions. Later, a green patina forms on copper outdoors with a varying intensity depending on where and how the surface is exposed. Over time, copper does not need additional technical maintenance, unlike paint.

How can fingerprints be removed from copper?

Grease, oil and finger marks can be removed by using low-alkali washing agents; even acetone can be used. This should be done as soon as possible after staining. Washing agents, including ammonia or chlorides, should not be used.
There are many commercial polishing chemicals available on the market. For example, a 5% citric acid liquid is an environmentally and user friendly option when polishing a slightly oxidized surface.

How can copper be coated to prevent staining and oxidation?

Clear coats help preserve the natural or mill finish. A clear coat may be as simple as a coat of wax or as advanced as a hi-tech acrylic lacquer. The choice depends on the situation. Clear coats are typically formulated to keep the metal very reflective, and their use is also intended to prevent tarnishing of the metal due to fingerprints and oxidation. One drawback is they are not permanent and will require maintenance over the years. Typically, clear coats applied to an interior feature will have a longer life than exterior applications, but they are subject to abrasion and may be susceptible to ultraviolet degradation.

How can staining of materials by copper be prevented?

Care should be taken when using copper above or close to mortar, cement, marble, stone and other porous materials. Copper runoff may cause bluish stains on these materials. To prevent such stains, the use of longer overhangs, sloping of copper surfaces away from other materials, gutters, and drip edges are all recommended.

What is galvanic corrosion and how it can be prevented?

Metals are rated according to their nobility ratings. When dissimilar metals are in contact with each other in the presence of oxygen and moisture, the more noble metal will corrode the less noble. Copper is one of the most noble of metals and must be separated from other less-noble metals. Contact between dissimilar metals should always be avoided. Painting, taping or gasketing with non-absorptive materials is also effective.
Care should be taken to prevent the wash from copper surfaces onto adjacent, exposed less-noble metal surfaces, since the traces of copper salts carried in the wash can accelerate the corrosion of less-noble metal.

How can graffiti be removed from copper?

Removing graffiti is challenging. Chemicals such as acetone are needed to remove paint. Very often mechanical abrasion is also needed to remove all graffiti from material. The dark oxide layer will be removed together with the graffiti, leaving a bright area. Copper-darkening chemicals are available on the market. The use of those may cause constant color differences between naturally oxidized and chemically treated areas. A good option is to wait and let the natural oxidation process cover the bright area with a new layer of dark oxide.

What are the environmental concerns regarding water run-off from copper roofs?

The risk assessment and 16 years of run-off studies for copper building sheets conclude that using copper as building material is totally safe for water, soil and agriculture.

How should copper materials be stored?

Copper for facades must be stored in dry conditions and at a constant temperature with low humidity. It must be protected against scratches resulting from dust, sand, etc. Direct contact with alkaline dust should be avoided, e.g. from screed, concrete, concrete saws, plaster, etc. because oxidation changes can occur. Direct long-term sunlight should be avoided because bonding of the film and the material surface can occur.

How should the copper material be installed?

If possible, the protective film should not be removed from the material during installation. If this is unavoidable, i.e. with edges, cotton gloves must be worn, in order to avoid traces of oil and excess salts on the copper surface. Before use, rubber gloves should be checked on a sample piece for wear and to determine if traces of material are left on the copper surface. During installation, hands must be kept oil-free. After completion of a facade (i.e. south side), the protective film should be promptly removed from the copper elements, if possible. Adhesive residue from the film may remain on the exposed side of the material as a result of intense sunlight and/or heat. Following installation, the film should be removed within 2 weeks.

What should be taken into consideration when working on copper?

When working on copper, the same metalworking tools as for aluminum and zinc can be used (e.g. shears that cut on the left and right). For patinated surfaces, the tool should be taped before use, in order to avoid spalling and scratches. Patinated surfaces are very sensitive and should be handled with the utmost care. In folded areas, spallings may naturally occur. These do not represent a defect or functional deficit.

How should copper facades be cleaned?

Nordic Copper facades should only be cleaned with cold water, without further additives. Windowsills can be cleaned with a damp cloth regularly (approx. every 4 weeks), in order to remove bird droppings or other deposits. Facade elements can be freed of dust and leaf debris with a water hose or pressure washer (at low pressure) approximately every 12 months. It is not advisable to use chemical cleaning agents, because these are very damaging to the copper surface and the already-existing desired weathering effect will differ significantly from the rest of the facade (discoloration, oscillation, darkening). When cleaning windows, care should be taken that no chemical agents come in contact with the reveals, windowsills and lintels, and the areas should be wiped off with a cloth afterwards. Holding on to copper window frames and facades can also lead to significant changes in the weathering effect, which cannot be completely removed. They can also be damaged when incorrectly combined with other metals.

More information can be found here:
Copperalliance resource library
Copperalliance copper-and-society/environment

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