Denim fabric is an off-white color in its raw state, so it is easy to bring denim to a pure white color. Unfortunately, most denim fabrics are treated with indigo dyes of varying intensities to create the wide array of blues most commonly known as denim color. Indigo-treated denim is harder to turn to white. While there is no way to dye denim white, you can bleach the fabric to get it close to a white color.
Mix one part bleach and one part water in a spray bottle.
Place a plastic tarp or towel on a flat surface.
Place the fabric flat on top of the tarp or towel.
Spray an even coat of the bleach and water mixture on the fabric, which will begin to change color immediately.
Let the fabric sit for 15 minutes to see the final color. If it is not white enough, spray more bleach and water on the darker areas until it changes to your desired color.
Immerse the fabric in the plastic tub or bucket filled with water. Rinse and wring two times, each time with fresh water.
Fill the bucket with water and half a bottle of white vinegar.
Immerse the fabric in the mixture and rinse. Wring the denim four times to stop the bleaching process.
Fill the bucket again with water only and immerse the fabric. Rinse and wring four times, changing the water each time.
Work outside or in a well-ventilated space.
Wear a surgical mask or scarf around your nose and mouth to avoid breathing in toxic chemicals.
You can also use a commercial bleach neutralizing product in the place of white vinegar.
If you start with light-colored denim, you will be able to get the color closer to pure white.
Both bleach and vinegar can significantly weaken denim fabric.
Black jeans are unlikely to turn white, turning a brown color instead.