Effectiveness of European oak wood staining with iron (II) sulphate during natural weathering

Arkadiusz Kwiatkowski,Agnieszka Jankowska

doi:10.4067/s0718-221x2022000100415

Arkadiusz Kwiatkowski, Agnieszka Jankowska

Open Access

https://doi.org/10.4067/s0718-221x2022000100415

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Abstract

Artificial graying of wood can be solution for contemporary trends of using uncoated wood for the arrangement of external architecture. The presented work was aimed at investigation of colour changes of European oak (Quercus sp.) wood surface treated with iron (II) sulphate. Three different procedures differing in time (2 h and 24 h) and temperature (20 Â°C and 70 Â°C) were used, as well as three different concentrations of aqueous iron (II) sulphate solutions (10 %, 20 %, 30 %). Beside the colour itself, it was evaluated the stained oak wood discolouration due to natural weathering. Thanks to iron (II) sulphate, wood colour changed to dark grey. In general, the colour changes on tangential section of wood were higher than those on radial section what was result of wood structure, in particular parenchyma cells arrangement in wooden rays. Contrary to expectations, the concentration of the iron (II) sulphate solution was not of significant importance for wood staining. Usage of concentrations higher than 10 % for the modification of the colour of wood gives the same effects. However, with increasing solution used to wood staining, the colour stability of the wood decreases during external exposure. The parameters of the procedure were not significantly affected. This allows the application of the simplest and least time-consuming modification method to be considered.

Highlights

According to the contemporary trends it is recommended to use untreated wood that turns grey after exposure to weather under aboveground conditions (Oberhofnerová et al 2017)
The presented work was aimed at investigation of colour changes of European oak wood surface treated with iron (II) sulphate as an attempt to verify the usefulness of the method on a wider industrial scale
As the colour change is not influenced by the iron (II) sulphate concentration, it must be concluded that the use of solutions with concentrations higher than 10 % is unproductive

Summary

Introduction

According to the contemporary trends it is recommended to use untreated wood that turns grey after exposure to weather under aboveground conditions (Oberhofnerová et al 2017). The decisive element for using different wood species in the harsh outside environment is their durability, in accordance with EN 350 (2016). In addition to the traditional interior design elements, the use of non-treated wood is expanding even further to external use. Willingness to use of non-chemical treated wood outside force to selection only wood of high durability. Many tropical species are considered to be the most durable wood. The use of tropical wood has several negative consequences including illegal deforestation as well as significant impact on climate changes (Swanna et al 2016). Among the European types of wood, the European oak heartwood is characterized by the greatest durability EN 350 (2016)

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