The more you wash denim, the more quickly the colour will fade. Washing jeans in hot water will make them fade even faster. The only way to make a pair of jeans darker is to use a commercial clothing dye product. These dyes -- available at some supermarkets and chemist's shops -- will quickly transform your faded or light-wash jeans into the dark-rinsed look you want.
Buy one to two packs of navy blue dye, depending on how dark you want the jeans to be. Don't purchase the denim blue shade if you want a dark wash. For an extremely dark blue colour, try using a navy blue dye along with a black dye.
Dissolve the dye powder into two cups of hot water. Stir the water to ensure that the colour is distributed evenly.
Fill a sink or bucket with extremely hot water, and add the pre-dissolved dye solution. For the best results, water temperature should be at least 60C.
Wet the jeans in hot water, then add them to the sink or bucket.
Leave the jeans in the dye bath for as long as the water remains hot (approximately one hour). The longer the jeans sit, the darker the resulting colour. Keep in mind that denim will look darker when wet.
Rinse the denim first in warm water, then again in cool water until the water runs clear.
Clean the bucket or sink with bleach or other commercial cleaning products immediately after removing the jeans to avoid staining.
Wash the jeans in cold water on a gentle cycle. Do not put other items in the washing machine with the jeans for this initial wash, as leftover dye may come off.
To keep your jeans dark, wash them in cold water only.
Follow the manufacturer's directions on the dye box.