Bold as brass - Copper alloy matches renaissance style

Materials World magazine
,
29 Oct 2012

A unique restoration project at the Uffizi Gallery in Florence, Italy, called for a special material to match its Renaissance style. Melanie Rutherford finds out why a copper alloy proved the perfect choice.   

The architecture of Italy’s many famous museums and galleries are often just as remarkable as the relics hidden within their walls. None more so than at the Uffizi Gallery in Florence – a Mecca for art lovers around the world, who flock to the prestigious gallery to view collections including Botticelli’s Primavera and Birth of Venus, and Titian’s Venus of Urbino.  

An intricate restoration project recently completed at the gallery employed 45 tonnes of brass and an ancient burnishing technique, in the construction of a new western staircase as impressive as the works of Da Vinci. The design was the brainchild of Italian architect Adolfo Natalini, who wanted to give the copper–zinc alloy, traditionally known for its golden colour, a distinctive dark, woody bronze colour that would work in harmony with the building’s traditional Renaissance style.  

Key to achieving this was a unique burnishing process originated in the Renaissance era, which gave the brass panels of the towering staircase their dark brown colour and antique aesthetic. The burnish, manually applied to the surface of the metal on-site by expert artisans, allowed Natalini to successfully blend modern design with traditional Renaissance philosophies.  

Says Monica Di Cosimo from copper manufacturer KME, which supplied the alloy for the project, ‘The designer was faced with a dilemma between conservation and renewal, and between adaptation and addition. He chose to combine metal and stone, two natural materials selected for their ‘true’ characteristics. The connection of brass, stone and glass are like three corners of a triangle, paralleling the Vitruvius definition of architecture – Ethos, Pathos and Logos, meaning structure, function and aesthetics. The use of natural products in their natural form is a leitmotif of the Natalini’s philosophy and makes his projects timeless.’ Natalini’s choice of brass enabled him to use such a natural material, while benefiting from its resistance, excellent technical properties and a high aesthetic value. ‘Copper-based materials last for centuries and require virtually no maintenance after installation,’ Di Cosimo explains.  

Step by step 
Logistically the operation was by no means straightforward. It took a total of 11,000 hours and 2,700 brass sheets to turn Natalini’s vision into reality, each 2mm thick panel cut to different dimensions and transported to the site one by one. Although this meant the material was supplied in several stages throughout the project, expert reproduction ensured uniform mechanical and chemical qualities and the same surface finish throughout each batch, ‘as if the brass was made by just one casting’, says Di Cosimo.  

The brass coils used to form the main structure of staircase were laser cut then precisely folded at KME’s Fornaci di Barga factory, near Lucca. Large brass panels were wrapped around the structure and its joints to form a continuous shape arising from the bottom step all the way up to the top.  

Staying true to the project’s philosophy, the bass was processed and treated on-site by ItalG, an Italian company specialising in the design and construction of architectural elements for the exteriors of historical buildings. ItalG’s unique processes for treating materials harnesses ancient technologies, the special burnishing process used for the Uffizi’s monumental staircase dating back to the 15th Century.  

The process is based on the works of Italian painter Cennino Cennini who, in his Libro dell’arte book of art, which he wrote in 1398, explains how to burnish metals to create the same effect as natural oxidation. ‘Some modern chemical products can help in term of safety, but nothing else has changed since then,’ says ItalG’s Sergio Tobia, who describes how the burnishing process posed a myriad of problems with regards to temperature, humidity and application, ‘solved with techniques we specially developed for the project based on Cennini’s suggestions.’  

Ageing gracefully  
Brass is a notably easy alloy to work with, its oxide mineral layer covering the surface of the large sheets offering a unique crystal-like consistency that Natalini chose to leave on the panels ‘to give a sense of life to something that is not living – another philosophical concept connected to the Renaissance’, explains Di Cosimo.  

Being electrochemically neutral, brass stays stable during chemical solicitation, a characteristic that avoids aesthetics problems such as fingerprinting. ‘It has a good mechanical performance, low thermal dilatation and it is easy to weld,’ says Di Cosimo, describing brass as ‘an architect’s best friend’. What’s more, the alloy will continue to react to its environment over time, gradually returning to its natural golden color under the touch of the Uffizi’s thousands of daily visitors.  

Staying faithful to the gallery’s powerful Renaissance style was a big ask for a comparatively modern design, calling for a material ‘with the same depth of perspective of the embossments of the Uffizi’s famous North Gate,’ says Di Cosimo, who insists this could not have been produced by any metal other than brass. For this unique project it proved ‘the perfect material – not only for such expressive works of art, but as an expressive material in itself.’   

Materials World would like to thank Bryony Samuel at the Copper Development Association, bryony. samuel@copperalliance. org.uk, Sergio Tobia at ItalG, sergio@italg. it, and Monica Di Cosimo at KME, monica. dicosimo@kme.com.