Fill a bowl with warm water and soda ash. Soak the article of clothing to be dyed in the bowl. Allow the item to soak for 10 to 15 minutes. This will make it easier for the dye to stick to the cotton.
Ring the item out. Make sure to remove all excess water.
Lay your item out on a flat surface. Pinch sections of the item and fasten them with rubber bands. Continue to twist and pinch sections of the item into as many sections as desired. If you desire to make an item all the colors of the rainbow, divide the item into seven sections.
Put on a pair of disposable rubber or plastic gloves. Dye that gets on your hands can be very difficult to remove. You may also want to wear old clothes and place newspaper under the area you will be working.
Dye your item. Squirt the colored dye into the various sections of your item. Make sure you are unable to see any white spaces on the item.
Place your item into a plastic bag. Keep your item in the plastic bag for one day.
Remove your item from the plastic bag. Rinse the item in cold water. This will remove any excess dye from your shirt prior to wearing.