The collected mangrove bark was dried in sunlight and later crushed to small pieces before being used for dye extraction. The dye extraction was performed by mixing the plant material and distilled water in the weight ratio of 1:10 and boiling for 1 h. After that, the resulting solution was filtered to remove the residue and the dye solution was separated into two portions: (a) one for evaporating under reduced pressure with a rotary evaporator, and (b) one for dyeing. The crude dye extract obtained from the rotary evaporator was dried and then stored in a desiccator before use. To obtain a standard calibration curve, the crude dye extract was later ground and diluted with distilled water. The dilution of the mangrove bark extract showed a relatively clear solution with a linear dependence on the concentration–absorbance relation at an absorption peak (λmax) of 278 nm. The concentration of 15 g L−1 was calculated from a standard curve of concentrations of the mangrove bark extract dye solution versus absorbance at the wavelength mentioned.