A Matter of Colour
A watch from Rado’s True Square Thinline Les Couleurs™ Le Corbusier collection (image: courtesy of Rado).
“Each of us has perhaps their colour,” reads a quote from Le Corbusier (1887-1965), blown up and printed on one of the gallery walls of Paris's Cité de l'architecture et du patrimoine museum. “[Often] we may not be aware of it, but our instincts are always right.”
Corbusier’s quote is part of the backdrop to a launch hosted in the museum by Rado, the Swiss watchmaker best known for its work with high-tech ceramic. Since 2019, Rado has worked in partnership with Fondation Le Corbusier, the body that oversees the architect’s legacy, to utilise Corbusier’s work with colour in contemporary products. In September, the Cité de l'architecture et du patrimoine, which lists a full-scale recreation of one of the apartment interiors of Corbusier’s La Cité Radieuse (1952) amongst its holdings, was deemed the ideal space to launch the latest release in Rado’s ongoing collaboration with the foundation.
This partnership is based around Corbusier’s Architectural Polychromy, a set of 63 colours that the architect specified in two colour collections that were launched in 1931 and 1959 – tones that he deemed “architectural, naturally harmonious and able to be combined in any way.” The first iteration of the Rado collaboration, which is mediated by Les Coulers Suisse, saw the company launch an edition of nine monochrome versions of its ceramic True Thinline watch, each executed in a single shade from Architectural Polychromy. For 2023, the approach has bee extended to the company’s True Square watch. Rather than vibrant monochrome editions, however, these new watches exhibit a quieter approach to colour – a neutral case, picked out with colourful accents on the watches’ indexes and hands, as well as the midlinks of the strap.
Image: courtesy of Rado.
Rado’s Le Corbusier watches appear simple in their treatment of colour, but this disguises the material complexity required by the process. “It’s very difficult to produce a specific colour in high-tech ceramic,” explains Christian Verdon, Rado’s head of R&D. A conventional ceramic, he explains, is produced using sand, feldspar or silica, which is ground down and cooked, resulting in a hard, but porous substance. Given this porosity, the material requires a glaze to seal it, and it is at this stage “where you usually put the colour”. A high-tech ceramic, by contrast, is formed from a finer aggregate of synthetic zirconium oxide, which is sintered at a temperature of around 1,500°C to create a material that, Verdon explains, “is completely dense and so doesn’t require a glaze.” As such, he continues, colour is added through the addition of pigment to the zirconium oxide before the aggregate is heated. “But not many pigments can survive that process.”
Organic pigments, Verdon explains, are simply “burnt up”, which leaves only metal oxides. These pigments, however, are “quite limited” in their range, Verdon says, with further restrictions brought in through regulations around which metal oxides can be exposed to human skin. Some colours are relatively straightforward to achieve through the pool of available oxides (“cobalt oxide for the blue,” Vernon explains, “chromium oxide for green”), but others present clear material challenges. A true red, Verdon explains, is impossible to achieve in a commercial ceramic watch, because the colour requires the use of cadmium, “which is not allowed to be worn on the skin for a long time.” Just as Le Corbusier suggested that each person had their own colour, so too do different materials – those which are chemically possible to achieve and those which are not. “Some things may seem simple,” Vernon explains, “but they’re not.”
Image: courtesy of Rado.
Within Rado’s wider work with ceramic, the company currently has around 40 colours that have been developed by Verdon and his team according to the material realities of ceramic. As regards the collaboration with Fondation Le Corbusier, however, the company was challenged to exactly match the shades specified within Architectural Polychromy – a steep challenge. Asides from selection of the base oxides, and the proportions in which they would be mixed, a number of other factors can also influence the precise shade in which high-tech ceramic emerges, the precise impact of which can only be determined through trial and error. “You also have oxidation state,” explains Verdon. “When you cook [ceramic] it is oxidised, but you can then take it into a reducing atmosphere, like hydrogen, which will also modify the colour.” The orange in the Corbusier collection (4320s in the Architectural Polychromy naming system), for instance, emerges from the sintering process “quite neutral”, Verdon explains, and only gains its vibrancy when subsequently exposed to hydrogen. These chemical considerations are further allied to practical ones. To achieve consistency in colour output, Rado requires extremely accurate ovens that can maintain an even and steady temperature, as even slight changes can radically alter the final shade of the material. “It's not difficult to mix the pigments accurately,” Verdon summarises, “but [everything] then depends on the temperature the material experiences during the cooking process.”
These are the challenges that lay behind Rado's work with Architectural Polychromy. Colour is not a simple finish that is easily applicable to a watch, but rather a chemical consideration that demands careful study, repetition, and navigation of material challenges. There is, Verdon adds, however, one saving grace in the development of a colour: “Once you know the exact recipe, you can repeat it again and again.” While Le Corbusier may have trusted in instinct when it came to colour, Verdon and his team place their trust in a different authority. In the case of high-tech ceramic, chemistry is king.
Rado paid for the writer’s travel and accommodation to visit the Rado True Square Thinline Les Couleurs™ Le Corbusier collection launch.
Words Oli Stratford