Iron is a great way to shift your naturally dyed fiber to darker shades quickly and easily. Make your own homemade iron water with 3 simple ingredients: rusty nails, white vinegar and water. After a few weeks, your iron water is ready to go! You only need a splash, so store it away to use any time you are looking for darker shades including gray and black. This video tutorial will show you how to make and use iron water, as well as the resulting color swatch samples of 6 different natural dyes on cotton.