If you want to tie-dye a cotton shirt, your best bet for long-lasting pure colour is to use standard fabric dye. Food dye works best with animal fibres such as wool; it has trouble clinging to plant fibres like cotton. However, if you’re going for a faded, pastel look or just want to try something new, feel free to experiment with food colouring, which can be found in the baking aisle in most grocery stores.
Combine 1 tsp vinegar, 20 drops of food colouring and one to two cups of boiling water in a glass bowl.
Fold, pleat or twirl the shirt into any shape you want and secure it with rubber bands. Vertical folds result in horizontal stripes, and horizontal pleats produce vertical stripes.
Put on the rubber gloves.
Dunk the shirt in the dye and stir it around with a metal spoon.
Keep the shirt immersed in the dye until the colour is slightly darker than what you want.
Rinse the shirt under cool tap water until it runs clear. Be prepared for a lot of the dye to seep out; this is part of the problem with using food dye on cotton.
Take off the rubber bands.
Dry the shirt with a hair dryer. The heat will help the colour to set.
Mix the standard colours in a package of food colouring (red, blue, yellow and green) to create a rainbow of colours for your tie-dye project. Use a decorator’s colour wheel to see which primary colours make up secondary and tertiary colours.
Do not expect your tie-dye design to last very long. The cotton won’t absorb much of the dye, and what it does absorb will leach out with each successive washing. Wool and silk both work better than cotton in terms of absorbing and holding onto dye.