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surface coatings. Within a few days of exposure to the atmosphere, a copper surface begins to oxidise, changing from the ‘bright’ mill finish to a chestnut brown, which gradually darkens over several years to a chocolate brown. Continued weathering can eventually result in the distinctive green or blue patina seen on older roofs.
The patina film provides impressive protection against corrosion, and can even repair itself if damaged, which accounts for the material’s longevity. A complex combination of factors determines the nature and speed of development of patina over time and this is much slower on vertical surfaces. It is not surprising that factory-applied surface treatments are popular to provide ‘straightaway’ oxidisation and patination of copper to a required level, particularly for facades.
Safety Having an A1 (non-combustible material) fire classification to EN 13501-1, copper is suitable for cladding tall buildings, using appropriate constructions of course. Low thermal movement makes it safe and straightforward to use in any climates and locations. Also particularly important today, copper is non-toxic and its inherent antimicrobial qualities make it ideal for touch surfaces, including interiors.
Natural processes
Many of the processes involved with copper are very similar to those already taking place in the environment. Copper mineral compounds, rather than chemical interventions, bring forward environmental changes without taking away the integrity of copper as a natural, living material. They form an integral part of the copper (and are not coatings or paint). Ongoing changes will continue over time, depending on the local environment, defining copper’s ‘living character.’
These surface treatments include pre-oxidised copper, where the thickness of the oxide layer determines the colour lightness or darkness. Alternatively, pre-patination utilises the same ‘brochantite’ mineralogy found in natural patinas all over the world. In marine climates, the natural copper patina contains some copper chloride giving it a blue-green colour, and this is emulated using 100% brochantite mineral. Alternatively, using a hint of iron sulphate yellow replicates greener natural patinas. With pre-patination, the process can be
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accurately controlled so that, as well as the solid patina colours, other intensities of patina flecks can be created revealing some of the dark oxidised background material to give a ‘living’ surface.
Copper alloys
Copper alloys have been used throughout history, with bronze and brass – which can also be pre-weathered – remaining popular for architectural applications. Innovative copper alloy gives a rich golden through- colour which is retained without developing a blue/green patina. It simply loses some of its sheen as the oxide layer thickens with exposure to the atmosphere, creating a protective matt finish.
Apart from traditionally jointed, rolled material supported by a substrate, various other forms of copper are increasingly being explored by designers. For example, copper can be supplied in profiled sheets or extremely flat honeycomb panels, pressed to provide surface textures and modulation, or perforated, expanded or woven as mesh, enabling transparency.
Graeme Bell is Nordic Copper sales and marketing manager at the Building, Construction and Architectural division of Aurubis
DELTA CENTRE, TARTU UNIVERSITY, ESTONIA Copper alloy fins with triangular perforations Photo: Maris Tomba
DEPTFORD LOUNGE, LONDON
Copper alloy cassettes in stretcher bond pattern with varying levels of perforation, providing transparency Photo: Chris Hodson
Copper can be recycled again and again without any loss of performance or qualities
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