<![CDATA[Teak leaves (Tectona grandis) are a potential source of natural dyes for textiles. This study investigated how dried teak-leaf powder particle size (40, 60, 80, and 100 mesh) affecs the optical characteristics, pH, and hot-water-extractable content of aqueous extracts and examined their application to cotton fabric. A completely randomized design with three replicates per particle-size treatment was used. Extracts were prepared in distilled water at approximately 60 °C for 1 h using a solid-to-liquid ratio of 1:10 (g/mL). Optical responses were measured using UV–Vis–NIR spectrometry over 350–950 nm, while pH and extractive content were evaluated using one-way analysis of variance. The largest absorption coefficients observed among the individual measurements were 4.192 cm⁻¹ at 391.1 nm and 4.075 cm⁻¹ at 575 nm, both in replicate II of the 100-mesh treatment. Particle size significantly affected extract pH (F(3, 8) = 18.96, p < 0.001), whereas its effect on extractive content was not statistically significant (F(3, 8) = 1.60, p = 0.264). The extracts colored alum-treated cotton fabrics, with visually observable differences among treatments. These findings indicate that particle-size selection can influence the optical response and pH of teak-leaf dye extracts; however, compound identification and quantitative textile colorfastness require further testing.]]>
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