Decoupling the dual source of colour alteration of architectural titanium: Soiling or oxidation?

The advanced structural properties of titanium, together with its fascinating interference colours, have opened the way to architectural applications as façade claddings. Yet, several problems of soiling and gradual corrosion tend to alter its aesthetic properties. Atmospheric exposure tests on titanium and anodised titanium were performed, and surface colour was monitored with spectrophotometry to evaluate both corrosion and soiling extent. In all cases, a slight surface oxidation was observed, which decreased with increasing initial thickness of the anodic film. The use of lightness as main parameter to quantify soiling must be carefully considered, as lightness variations must also take into account the influence of oxide hue variation.