Chestnut shells were thoroughly washed with water and then dried under the sun before extraction. They were ground in a pulverizer and then screened through a sieve with a mesh size of 60. Dye extraction was performed by mixing the powdered sample and distilled water at a weight ratio of 1:20 and then boiling the mixture for 30 min. Manual stirring around 60 rpm was done to disperse the chestnut-shell powder in the liquid during extraction, as the mixture had a high liquid-to-solid mass ratio. Extraction was performed twice. The supernatant from each experiment was collected and condensed under reduced pressure in a rotary evaporator to remove the solvent. Finally, the concentrated solution was dried in a drying oven at 50 °C to obtain a brown pigment. The pigment was freshly prepared before analysis. The extracts were analyzed by measurement of the wavelength of maximum absorbance, λmax, on a UV–vis spectrophotometer. The spectrum is shown