Wood has been used for various purposes for many millennia. Recent trends in architecture and environmental policies have increased the demand for natural, unprotected wood in outdoor applications. However, wood exposed to the elements tends to grey unevenly, which can be problematic for visually important applications like timber façades. One solution is artificial greying with iron ions, providing a uniform colour that later transitions to natural greying. However, these shades differ from naturally aged wood. If the wood is pre-aged before the iron ions are applied, the surface develops a greyer shade. In our study, we investigated how different accelerated ageing treatments affect the final appearance of wood after iron ion treatment and natural ageing. The pre-treatments included UV radiation, leaching and tannin treatment. After accelerated ageing, colour differences increased in proportion to the time of UV irradiation, while the leaching process did not play a significant role. After the iron ion treatment, the highest colour differences were observed on the tannin-treated samples. After outdoor exposure, the colour differences between the different pre-treatments decreased over time. The weather is also an important factor, as high levels of sunshine and rain resulted in a significant lightening of the specimens after 18 weeks of outdoor exposure. This is also when the first blue stain fungi appeared, whereas the control samples already showed them earlier. FTIR analysis proved the influence of pre-treatment and natural ageing processes on the chemical surface composition.
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