Change the look of your favourite jeans or create a fashion statement from thrift-shop finds by dyeing blue denim black. Commonly available dyes such as those from Rit brand are easy to use in your home washing machine. This method will dye your jeans or other cotton trousers a deep, uniform black.
Wash your cotton or cotton blend jeans using unscented washing powder. Use stain remover, if necessary, but do not use fabric softener. Leave the jeans wet if you are going to dye the jeans right away. Dry them if you are going to dye them at a later time, but do not use dryer sheets. Wet the dry jeans evenly with hot water in the sink before dyeing.
Put on rubber gloves and empty three boxes of Rit brand dye---either three boxes of black dye, or one box each of dark green, cocoa brown, and scarlet---in a large glass bowl, using at least 2 cups of hot water per package of dye. Stir with a metal spoon until dissolved. Add 1 cup of kosher salt to the bowl, and stir until that is dissolved.
Fill the washing machine with hot water. Still wearing gloves, pour the dye, salt and water combination from the glass bowl into the washing machine. Add 1 cup white vinegar and 1 tbsp liquid washing powder, and agitate for a few moments to mix thoroughly.
Place the wet jeans in the dye mixture in the washing machine. Set to agitate, and keep turning the washer dial forward to the next agitation cycle to ensure that the jeans remain in motion in the dye for at least 30 minutes. Allow the rinse cycle to run through, then remove the jeans and rinse them thoroughly in the sink until the water runs clear.
Wash the jeans with detergent in the washing machine on warm, then remove and place in the dryer or hang to dry. Clean your washing machine by running several cycles through without clothes in them (or with clothes you do not mind acquiring possible remnants of the dye, such as other black clothing), using washing powder and 1 to 2 cups of chlorine bleach. Wipe down the lint trap on the dryer and any additive trays on your washing machine with a bleach solution.
You can dye jeans any fashion colour using available shades of Rit dye, or combine colours to create your own effects. Make sure your jeans are clean and thoroughly, evenly wet before lowering them into the dye, or they may dye unevenly. Alternatively, to create a tie-dyed textured look, rub soap or paraffin wax on some areas of the jeans, which creates resistance to the dye in those areas, leaving them close to the original colour. You can dye other cotton or linen clothing following these steps.
Wear gloves when handling dyes, and wear a mask or damp cloth over your face if you have respiratory concerns. Keep dyes, both in the original powder form and once mixed, out of reach of children.