Black jeans are denim dyed black rather than the traditional blue colour. Black jeans fade from repeated washing. Every time the black jeans go through a wash cycle some of the dye releases into the water. There are a few ways to minimise the fading process including washing the jeans inside out, using only cold water or using a washing powder that locks in colour. All have some effect, but the black will still fade. Technically, there is no way to unfade any fabric colour because fading is the process of permanently losing colour. There is a way to restore the black colour to the jeans.
Choose any brand of black fabric dye. Read the manufacturer's recommendations to determine the amount of dye necessary to achieve your desired colour.
Add powdered dye to a small bucket. Add hot water to dissolve the powder. Allow the mixture to sit until it completely dissolves.
Add water according to the manufacturer's directions, generally 3 gallons. Stir the dye into the water to mix it thoroughly. Use the warmest water that is safe for the fabric and suggested by the dye manufacturer.
Place the jeans in the bucket. Keep the jeans in constant motion to allow the dye to disburse evenly throughout the fabric. Use a clean broomstick handle or other stick to swirl the jeans in the water. The length of time depends on the depth of colour you want to achieve and the package directions. Generally, fabric can soak for up to one hour.
Remove the jeans from the water. Rinse them with warm water immediately followed by cool water until the rinse water becomes clear.
Launder the jeans in the washing machine. Use warm water and mild laundry soap. Rinse in cool water.
The longer the jeans soak in the dye water, the deeper the resulting colour. Wear gloves when touching dye water.