Identify the type of fiber your rug is made out of. This will dictate the type of dye and dyeing process you use, and it is usually located on the rug tag. Purchase enough dye for the weight and fiber content of your area rug. Consult the dye manufacturer's website and the dye directions to ensure that you have plenty of dye beforehand.
Fill a large sink with hot water so that your area rug can float freely in the water with plenty of room to spare. Just prior to dyeing, add several large potfuls of boiling water, which will give your rug a much better color result. If you are using a powder dye, predissolve the dye in 2 cups of boiling water. Add the amount of liquid or predissolved dye required for your rug. Stir the dye bath with a wooden stirring stick to evenly spread the dye.
Completely submerge your rug in clean, hot water. Your bathtub or shower works well for this purpose. Ensure that all fibers of the carpet are soaking wet with hot water.
Transfer your area rug to the sink containing the dye bath. Lower it carefully into the water while wearing rubber gloves to protect your hands. Leave the rug in the dye bath for up to 30 minutes, stirring the water constantly. Take the rug out when it has reached the desired color. If it isn't dark enough, make another dye bath with one and a half times the dye you used in this bath and soak for up to another 30 minutes until your color is achieved.
Unplug the sink drain and allow the dye bath water to run out. Rinse the area rug thoroughly with warm water to remove all excess dye and continue rinsing until the water runs clear. Transfer the rug to your washing machine and wash with gentle laundry detergent and warm water.
Clean your sink with bleach cleanser to remove excess dye. Air dry your area rug. Do not use until completely dry.