To remove black walnut stains from washable fabrics, sponge the stain with water, apply a few drops each of dishwashing detergent and white vinegar, cover with a paper towel, let the garment stand for five minutes, and rinse with water. Repeat again if necessary to finish removing the stain.
For color-fast fabrics that are safe to bleach, remove any residual black walnut stains by applying a bleach solution made from 1 tablespoon of water to 1 teaspoon of bleach. Allow the solution to remain on the fabric for two minutes, rinse with water and reapply as necessary. Apply a solution made from 2/3 cup of water and 1/3 cup of white vinegar to remove any residual bleach. Rinse the fabric again.