As a listed building, careful attention has been paid to many different elements of Miesian Plaza during its ongoing redevelopment, including the exterior bronze cladding work on the building. While the Miesian Plaza Design Team was not obligated to treat the existing bronze cladded façade, since it had not deteriorated significantly over the last 40 years, it was decided that in order to execute a holistic approach to improving the design, each exterior spandrel panel and rib would be removed and treated to create a uniform, stable patina.
Once all of the bronze was treated, it needed to be accurately returned to its original position, to maintain and optimise the appearance of the listed façade.
In order to achieve their goal of optimising the entire exterior façade, the Miesian Plaza team consulted with experts to clean all of the bronze cladding, and bring it back to its raw metal base. A specialist treatment was also applied to secure a consistent coating, or patina, which would ensure that the original design intent for the façade patina was maintained. With regards to specific colour, the original intention was to maintain a colour over the façade that resembles an old penny. This rich brown colour would then be complimented with natural highlighted hues throughout the building complex.
Detailed Material Overview: Composition of Bronze Cladding
To give a detailed material overview, all external metal cladding in the Miesian Plaza complex is solid bronze, which is technically an alloy of copper and 100% recyclable, which adds to the improved environmental rating of the building. In fact, to expand on the idea of recycling even more, there is no limit as to how many time copper and copper alloys can be recycled, as they are considered to be a renewable finite material. In addition to that, recycling copper only requires 15% of the total energy otherwise consumed in activities like mining, milling, smelting and refining raw metal.
Therefore, copper and copper alloys are some of the most resource efficient cladding materials available, and have been for hundreds of years. Copper is also recognised for durability, resistance to corrosion, low maintenance and recyclability. Copper is also non-toxic and biostatic, which means that no bacteria will grow on its surface. While no material deterioration had occurred over the last forty years, a certain patina had begun to discolour.
Patinas and Cladding: Miesian Plaza
While a general appreciation for the bronze coloured façade might suffice, we thought it would be an interesting exercise to explore the term “patina” and “cladding”, and how they have been used in order to understand the process and how it can differ in various applications.
A patina is thin film or coating formed on the surface of a metal, often by way of a chemical reaction. This film creates a barrier which prevents the metal below from reacting further, thus protecting it and stabilising it. At Miesian Plaza the patina being created on the bronze is both aesthetic and functional, affording a uniform appearance and protection of the metal.
Cladding, in the strictest sense, is the act of physically bonding one metal onto another in order to protect the metal beneath, but in construction cladding will generally refer to the outermost skin of a building (e.g. wood panelling, glass, bricks) which acts to protect the internal elements. In the case of Miesian Plaza, the cladding is a curtain wall comprising of glass and bronze.
Environmental Factors and Restoration
Many environmental factors can contribute to the appearance of bronze and patinas, including elements such as humidity, temperature, ultra-violet light, proximity to the ocean, air pollution and even what plants and animals can be found in the area. Acid rain in particular is known for affecting the appearance of bronze because of its sulphuric acid content which leads to streaking. Human contact is also a consideration, which would be more appropriate in the case of a publicly accessible bronze sculpture, for example.
Past methods of bronze restoration include chemicals and electrolysis, but this approach can often be very severe, as it removes the patina and can damage the appearance and make the bronze porous, especially in the case of bronze sculptures exposed to the elements. While a variety of methods have been used to treat and conserve bronze, some of the most prized historical bronze objects have not been treated at all to preserve the original patinas, such as ancient Chinese artefacts.
In the case of Miesian Plaza, bronze cladding was used on the building’s exterior, so would not have easily been exposed to human touch, but in the inclement climate of Dublin and Ireland in general, would have had significant exposure to rain, which if affected by high levels of sulphur dioxide from industrial pollutants like burning fossil fuels, could potentially have contributed to some kind of effect on the patina of the exterior bronze.
Insight into Bronze Cladding: Seagram Building, New York
In the case of the Seagram Building in New York City, the patina or bronze cladding has also been used for aesthetic value. In particular, it has been said that the bronze colour used in the glazing of the Seagram Building was to create an aesthetic link to the colour of whiskey, the main product sold by the Seagram company at the time, and the bronze then coloured to emulate an old penny.
As mentioned before, the design of the Seagram Building was an inspiration for the original Miesian Plaza design. This is in terms of both the exterior elements and the ambience that the original architects wanted to achieve: steel and glass building in the post-industrialist Miesian Style that created a Manhattanesque streetscape in Dublin, and an associated feeling of pace and freedom of movement. The bronze cladding was also used to echo the hidden internal structure of the building underneath.
In fact, the Seagram Building represented a revolutionary approach to skyscraper design at the time, with the integration of the exterior and interior space, and not following the usual pattern of people accessing the building straight off the street. This is an ideal which is being fully integrated into the redevelopment of Miesian Plaza as a contemporary, urban workspace. The repatination of the façade gives the bronze a uniform appearance, contributing to the overall aesthetic of clean, modern design.