Extracting color from a dark fabric using bleach is called "discharging," and the process works well on natural fibers like cotton, linen, silk, wool or any blend of the four. It does not work on synthetics such as polyester, acrylic, nylon and spandex. Other synthetics, like rayon, may go only a shade lighter. When you want to transform a black shirt into a gray shirt, bleach may accomplish the task. Spraying the bleach directly on the fabric in a well-ventilated area will give you control over the process, while hand or machine washing can cause streaks and blotches.
Test the fabric by cutting a small swatch from a hem or seam. Place the swatch in a glass dish and use a cotton swab or paper towel to dab bleach on it. If the fabric turns yellow or pink, you will not be able to achieve a shade of gray using bleach. If the fabric turns gray, continue with the process.
Put on old clothes and set up your work area in a ventilated area, such as a porch or driveway. Cover the area with an old bed sheet or plastic. Pour 8 ounces of bleach into the spray bottle and fill it with lukewarm water. Shake the bottle gently to mix. Fill the bucket with 4 gallons of water and 1 1/2 cups of hydrogen peroxide or bleach neutralizer. Stir.
Remove buttons and other embellishments from the shirt. You can sew them back on later or change them to something new. Wet the shirt with water and wring it out so it's damp. Spread the shirt onto the work area and smooth it out with your hands. Put on rubber gloves. If you are sensitive to fumes, put on a face mask as well.
Set the timer for eight minutes. Spray the shirt with the bleach mixture, moving from the top to the bottom. Saturate all areas. Flip the shirt over, flatten, and repeat. Work quickly so that the shirt is absorbing bleach consistently.
Observe the bleach lighten the fabric. Respray any areas that are blotchy or streaked. After eight minutes or when it is slightly darker than the desired shade, submerge the shirt into the bucket containing the hydrogen peroxide or bleach neutralizer mixture. Allow it to soak for 10 minutes.
Rinse the shirt with lukewarm water in a sink or tub. Wring it dry and wash it in the washing machine with an old towel or sheet. Dry it and replace the buttons or other embellishments.