Wood finishing using natural dyes is gaining increasing attention due to growing interest in sustainable materials and eco-friendly processing. Poplar (Populus sp.), as a widely used light-coloured and absorbent wood species, provides a suitable surface for testing coloration techniques using natural substances.
This topic is important because conventional synthetic dyes used in wood finishing often pose environmental and health risks. Natural dyes, by contrast, are biodegradable and non-toxic, making them ideal candidates for greener production methods.
Previous studies have explored the application of natural dyes such as indigo, madder, or turmeric on textiles, and more recently on wood substrates. However, the comparative performance of dyer’s madder (Rubia tinctorum) and dyer’s woad (Isatis tinctoria) on wood, especially poplar veneers, remains underexplored.
A gap exists in understanding how these two dyes differ in terms of visual and measurable colour outcomes when applied to wood veneers, particularly under controlled conditions and with the use of mordants.
This paper addresses this gap by presenting a comparative study of colour intensity, hue, and mordant effect on poplar veneer staining using aqueous extracts of madder and woad.
Experimental
Materials
Poplar veneer sheets (90 × 70 × 0.6 mm) were used. Two natural dyes were applied: woad (Isatis tinctoria L.) collected near the Vistula River (Warsaw) and madder (Rubia tinctorum L.) purchased from DZIKIE BARWY. Woad was used fresh (150 g in 200 ml water) and dried (3.75 g in 150 ml), heated at 80 °C for 10 h. Madder (75 g in 1.5 L water) was heated at 80 °C for 2 h and distilled. Five 300 ml madder dye variants were prepared with 12 g of extract each.
Surface Mordanting
Samples were mordanted in crystallisers with:
– Distilled water (control),
– 2% alum,
– 2% citric acid (woad only),
– 3% vinegar (woad only),
– Iron(III) sulfate,
– Iron(III) sulfate + citric acid,
– Soda ash (madder only).
Woad samples were heated at 95 °C for 1 h, madder at 80 °C for 1 h. All were dried at 75 °C for 15 min.
Colouring
Woad dye was mixed with 15 ml of 25% ammonia, rested 10 min, then used to dye veneers at 55 °C for 1 h. Madder staining occurred simultaneously with mordanting. All samples were surface-dried and dried again at 75 °C for 15 min.
Colour Measurement
CIELAB values (L*, a*, b*) were measured using ERICHSEN SPECTROMASTER 565-D. Colour difference (ΔE) was calculated. Measurements were taken at 3 fixed points per sample (≥9 readings/sample).
Conclusions
This study demonstrated that poplar veneer can be effectively stained using natural dyes derived from Isatis tinctoria L. (woad) and Rubia tinctorum L. (madder). Each dye produced distinct and visually appealing coloration: woad yielded shades within the blue spectrum, while madder produced warm red tones. The use of mordants significantly influenced dye absorption and colour intensity, with iron- and alum-based mordants providing the most pronounced effects. Colour measurements confirmed clear differences in CIELAB parameters depending on the dye and mordant used. These results highlight the potential of natural dyes as sustainable, low-toxicity alternatives for wood finishing processes, offering both environmental benefits and aesthetic diversity.
Keywords: veneer, natural dye’s, dyer’s woad, colour change, dyeing
Authors
Nikola Kucharczyk
Faculty of Wood Technology, Warsaw University of Life Sciences – SGGW, Warsaw, Poland
Jan Szadkowski
Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences—SGGW, Warsaw, Poland
Radosław Auriga
Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences—SGGW, Warsaw, Poland
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