The Effect of Natural Colourants in Woad (Isatis tinctorum L.) on the Dyeing Properties of Oak and Poplar Wood

The aim of this study was to investigate the potential of dyer's woad (<i>Isatis tinctoria</i> L.) as a sustainable, plant-based colouring agent for enhancing the visual properties of wood surfaces. Veneers of oak (<i>Quercus</i> sp.) and poplar (<i>Populus</i> sp.) were used as materials and dyed with aqueous extracts derived from fresh and dried woad leaves. To facilitate dye uptake, the veneer surfaces were pretreated with various mordants: alum, citric acid, acetic acid, and distilled water (as a control). The aim was to assess the impact of both the form of the plant material and the type of mordant on the resulting colour change. Colour modifications were measured using spectrophotometry and subjected to statistical analysis. The results revealed distinct differences between untreated and dyed veneers, as well as among samples treated with different mordants. Furthermore, the effectiveness of the dye varied depending on whether fresh or dried leaves were used. These findings confirm the feasibility of employing <i>Isatis tinctoria</i> L. as a natural wood dye and highlight its potential as an eco-friendly alternative to synthetic surface treatments in decorative wood applications.