Copper – the inside story

Graeme Bell of Aurubis says that copper has a wide range of uses in architectural interiors alongside external applications, and explores the various surface treatments available

Copper has seen a dramatic change from its historic role in roofing prestigious buildings to a thoroughly modern external skin for contemporary architecture. And its role as an interior surfacing material is growing as well, with a surprising diversity of natural colours, patterns and textures, inviting innovation from architects, blurring distinctions between inside and out.

Copper and its alloys – such as brass and bronze – enjoy unique characteristics, particularly in terms of safety, sustainability and long-term performance, wherever they are used. Copper is also safe to handle, as well as being non-brittle and predictable to work. With an ‘A1 (non-combustible material)’ fire classification to EN 13501-1, copper is inherently fire-safe and suitable for cladding tall buildings, using appropriate constructions. It is also, therefore, rated ‘Class 0’ for surface spread of flame, making it suitable for wall and ceiling surfaces in communal areas. Particularly important today, copper is non-toxic, its inherent antimicrobial qualities making it ideal for touch surfaces.

Copper’s exceptional longevity – it’s conservatively regarded as having a 200 year life – is due to the patination process which ensures extreme durability without maintenance and resistance to corrosion in virtually any atmospheric conditions. This natural development of a distinctive patina when used externally defines the material, with colours changing over time dependent upon local environmental conditions, including rainfall and air quality.

Within a few days of exposure to the atmosphere, the surface begins to oxidise, changing its colour from a ‘bright’ mill finish to chestnut brown, which darkens over several years to a chocolate brown. Continued weathering can eventually result in the distinctive green or blue patina seen on older roofs. Obviously, copper used internally or sheltered from rainfall will not change and develop in this way.

A ‘living material’
Modern factory-applied surface treatments can provide ‘straightaway’ oxidisation and patination of copper surfaces to a selected level – and these can also be used internally. Essentially, they bring forward the environmental changes without taking away the integrity of copper as a natural, living material, and are not coatings or paint. Some of the processes involved are very similar to those taking place in the environment and utilise copper mineral compounds, not ‘alien’ chemical actions.

These processes can enable designers to determine both the colour and intensity of patina for each project from the start. As well as a solid patina colour, other intensities can be created, revealing some of the dark oxidised background material as ‘living’ surfaces.

Alloys of copper have also grown in popularity. They include bronze, an alloy of copper and tin which gradually changes to a dark chocolate brown when used outside, and brass, which can also be supplied pre-weathered. An innovative alloy of copper with aluminium and zinc enjoys a rich, golden through-colour which remains very stable, just developing a matt surface – but no patination – over time.

As well as roofing and external cladding, copper and its alloys are also the metals of choice for interior design, contributing a distinctive tactility to door furniture and handrails, and a visual richness to lighting and other fittings, championed by leading designers such as Tom Dixon. Increasingly, they are being applied as high-quality finishes for walls, doors, ceilings, elevators, highlight surfaces, bars, splashbacks and counters, exploiting the materials’ unique performance characteristics.

Mechanically applied surface treatments
Most recently, various copper surfaces and alloys have been made available with a diversity of mechanically applied surface treatments, adding an extra dimension. The latest developments in abraded and embossed mechanical surface treatments are particularly suited to interior design, adding another level of close-up visual richness, texture and tactility.

These treatments include embossing to provide regular patterns of raised or recessed forms, some also abraded to reveal highlights of the base material colour for additional design effects. Grindings are also available with linear, cross-hatched or curved-swirl hairlines to give distinctive matt surfaces. These surface treatments, combined with the natural living colours of copper and its alloys, offer real design freedom, adding a richness and opulence to public areas. They can also provide an inherent warmth and sense of quality to ‘highlight’ surfaces in homes as well.

Forms & systems
Apart from traditionally-jointed, rolled material supported by a substrate, various other forms of copper are increasingly being explored by innovative designers. For example, copper can be supplied in profiled sheets or extremely flat honeycomb panels, and it can be pressed to provide surface textures and modulation. The material can also be perforated, expanded or woven as mesh, giving varying degrees of transparency. When used internally, of course copper can be used in an even wider range of forms and systems, free from the constraints of weather-proof detailing.

One particular recurring architectural theme is material continuity, blurring the boundaries between outside and in with external copper cladding simply continuing past fully-glazed walls. When used outside, it’s important to remember that ongoing changes to copper, including pre-oxidised and pre-patinated, as well as alloys such as brass and bronze, will continue over time depending on the local environment. Again, this does not generally apply to interior applications and designers should understand and, indeed, celebrate the divergent developments of internal and external copper.

Graeme Bell is Nordic Copper sales and marketing manager at Aurubis