This study investigated the potential of sumac leaves as a natural mordant for weld-dyed cotton batiste. Sumac leaves at different concentrations (50-200%) were tested alone and in combination with aluminum acetate as a control. Colorfastness to laundering was evaluated. Results showed sumac leaves darkened the dyed fabric and lowered brightness compared to the control. However, gray scale ratings for color change and staining improved with higher sumac concentrations, with 200% sumac and aluminum acetate showing the best rating. While sumac leaves have potential to increase colorfastness, more research is needed to optimize maintaining the dye's original color.