Colour chemistry of steamed and boiled walnutwood (Juglans regia L.)

Wood colour change in hydrothermal processes is one of the phenomena which can be intentionally induced, but the final result is much influenced by empirical knowledge, which is difficult to explain chemically in most cases. The chemistry of wood colour change is extremely complex and many different factors influence the change of one of the primary properties of wood – its colour, and hence also its aesthetic value expressed through its market price. The closer the colour gets to the target one, and the better its uniformity, the greater is its aesthetic value, and consequently the higher the price of final products. In practice there are steaming and boiling processes of solid wood for induced colour change, especially for wood types with pronounced heartwood. Numerous researches have been performed in the field of colour change and its chemistry. However there is a lack of connection between chemical laboratory researches and everyday industrial practice. The aim of this work is to present an overview of the basic research methods of colour changes, as well as influencing factors and chemistry of hydrothermal
processes of several wood types and particularly of walnut wood.