How to Dye Fabric Black Naturally - Natural Black Fabric Dyes -Covering rusty iron nails with vinegar will produce a chemical reaction that produces a black dye. Simply fill a non-reactive tub with the nail and vinegar. When ready to dye, remove the nails using a strainer. Other iron hardware - such as hinges, fence parts - can also produce the same reaction. Once the fabric has reach the color desired, the black dye must be set into the fabric using alum to make it permanent.