"Crocking" is the term used in the textile industry to describe the process of dye being removed from fabric by rubbing. For example, the indigo dye used in denim blue jeans can end up rubbing off, or crocking, and giving you blue-tinted legs. It can also stain your furniture and light-colored clothing. You can help prevent crocking by setting indigo dye in fabric using a few simple household items.
Set a washing machine to fill with cold water and add a capful of liquid delicate laundry detergent. Put the indigo fabric in the washer when it is about half full. Allow the wash cycle to run, but stop the washer before the rinse cycle begins.
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Add 2 cups white vinegar to the rinse water, but do not let the rinse cycle finish yet. Soak the fabric in the vinegar solution for a minimum of two hours.
Turn the washer back on and let it complete the rinse cycle.
Drape the fabric over a clothesline and let it air-dry.
Set a steam iron to the hottest setting recommended by the fabric manufacturer and press the fabric all over. The heat and steam will further help to set the indigo dye.