Outdoor wood is exposed to various factors that cause the wood to grey or age. The ageing processes can vary greatly depending on the exposure. Parts of the wood that are not exposed to external factors, e.g. under the eaves, are less exposed and the ageing process is therefore slower. This can be accelerated by solutions based on iron ions. In this way, the wood greys quickly and evenly. However, the colour after iron treatment also depends on the previous ageing of the wood. In our study, we observed the colour change as a function of outdoor weathering. Before treatment, the samples were exposed to outdoor weathering for different periods of time and then treated with a 5% solution of pure iron(II) sulphate and commercial iron(II) sulphate (green vitriol). We found that the ageing time affected the colour change, as the samples stored for 5 weeks before treatment were closest to the colour of naturally aged wood. At the beginning of exposure, iron(II) sulphate protects against mould growth, but after 2 months blue stain fungus starts to grow on the treated samples as well. The growth of blue stain fungi on the treated samples did not significantly affect the colour and visual appearance of the wood treated with iron-based solutions.

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