What can I use to dye clothes black?

Try making a black dye out of iron and acorns that you can use on your clothes! Start by placing 2 handfuls of rusty objects like nails, screws, or bolts into 1 cup (240 ml) of vinegar in a jar. Then, fill the jar 3/4 of the way with water and seal it. Set the jar in the sun for 1 to 2 weeks until the liquid is orange. Add 5 pounds (2.3 kg) of acorns per 1 pound (0.45 kg) of fabric, place the acorns in a large pot, cover them with water, and let it simmer for 1-2 hours. Add your fabric to the acorn pot for 20-45 minutes, then remove it and soak it in a pot with the vinegar and iron mixture for 10 minutes. Alternate soaking the fabric in the dye and the iron until it's as black as you want it to be.