Colouring fabric is easy if you have the right dye. You can go to any arts and crafts store and pick up a bottle or packet of dye, but it probably won't be environmentally friendly. If you're looking for a way to dye fabric black with natural materials, use oak galls. Oak galls are growths on oak trees and appear similar to nuts. When crushed and boiled, oak galls make an easy black dye.
Collect about 40 oak galls from an oak tree. The galls are spherical in shape, have tiny "horns" or bumps protruding from them and are typically dark brown and grey. They can simply be pulled or snapped off of twigs or branches.
Pour 4 cups of cold water into a sauce pot. Add 1 cup of vinegar to water. Place the sauce pot on the stove and bring the water to a simmer. This mixture will be your colour fixative to make the colour set in the fabric.
Place the fabric you wish to dye into the sauce pot. Leave the fabric simmering in the fixative for one hour. While the fabric is simmering, start working on the dye.
Chop the galls up using a kitchen knife until you have 2 cups of galls.
Place the galls into a separate sauce pot with 4 cups of water. Turn the burner on high. When the water starts to boil, lower the temperature to allow the water to simmer the galls for one hour.
Remove the fabric from the fixative after one hour. Rinse it under cool water. Wring out excess water.
Place a strainer over the top of a bucket. Carefully pour the water dye into the strainer to separate the dye from the chopped galls. Pour the water dye, or dye bath, back into the sauce pot.
Place the wet fabric into the dye. Turn the burner on low and keep the dye simmering. For a stronger shade of black, leave the fabric in the dye bath over night.
Take the fabric out when the desired shade is reached. Rinse the fabric out under cool water until the water runs clear.