Cotton takes readily to common dyes found at the grocery store. There are a number of ways you can dye cotton pants, but the two most used are the washing machine and the stovetop method. Of the two, the stovetop method gives a more vibrant color, especially when dying a dark color. Either way, both are simple to accomplish and the process can be performed in an hour or less.
Washing Machine Method
Dissolve the dye into 2 cups of hot water in a bowl, if using powdered dye.
Fill the washing machine half full of hot water.
Add the pre-dissolved dye or up to one bottle of liquid dye to the water.
Wet the cotton pants thoroughly with hot water and place in the dye bath.
Set your washer for the longest cycle. The pants should remain in the dye for at least 30 minutes. If needed, stop the machine before the rinse cycle and restart the cycle to get the time needed.
Rinse light colors in cold water until the water runs clear. Darker colors should be re-washed in warm water with detergent and rinsed in cold water.
Dry as normal by either using a dryer or clothesline
Stove Top Method
Fill a stockpot or other large vessel with hot water. You will need 3 gallons of water for every pound of clothing you will dye.
Dissolve powdered dye in 2 cups of hot water and pour into the stockpot. If using liquid dye add 1/2 bottle of dye for each 3 gallons of water.
Wet the cotton pants in hot water and place in the stockpot.
Bring the dye solution to a simmering boil and stir with a wooden spoon for 30 minutes.
Rinse in warm water until the water runs clean and rinse a second time in cool water. Dry as normal or hang on a hanger, clothes rack or clothes line to dry.