The shirt should be washed at least once and dry before you begin. If the garment is damp, the paint will spread out more.
Protect your table with plastic and wear gloves.
Place the T-shirt on the plastic and spread out the fabric as much as possible. Then fold the shirt in half vertically.
Draw half of a heart along the folded edge with a self-erasing marker (the line will disappear after 48 hours).
Sew the fabric together with a slightly thicker thread along the line, up from the heart and down. Leave a long enough tail of thread so that you can tighten up the heart. Tighten the heart together while turning the fabric, so that the seam forms a straight line.
Tie together with a piece of cotton string, straight across the tightened seam. Wrap a rubber band over it as well.
Use a plastic pipette to drip paint onto the fabric. You can also mix colours together to make new shades, for example, with one colour on the heart and mixed colours outside of it. If you like, place a rubber band outside of the heart too, or just drip a little paint here and there. Squeeze the fabric with your fingers so that the paint spreads inside of the fabric bundle.
Leave the garment in the plastic for 12 to 24 hours. Unfold the fabric and let it dry flat.
When the shirt is dry, fix the paint with an iron set to cotton without steam for 5 minutes.*
Then it can be machine-washed at 40°C max, and should be washed inside out. Wash the shirt separately the first few times after painting or dyeing.
Reinvigorate an old T-shirt with fabric paint! Keep in mind that the paint will spread out more if the garment is damp, so to create a distinct heart, it is best if the shirt is completely dry when you dye it. Choose whether you want to place rubber bands around the rest of the shirt too, in order to create a distinct tie-dye pattern, or if you would rather have a flowing pattern and only drip colour here and there. Either way, you are sure to have a unique result. This thin fabric paint can be used with clothes that are made of at least 50% cotton (or silk).
*Alternatively, fix the dye in the oven (not silk) at 150°C for 5 minutes, but make sure the garment has no buttons, elastic, or heat-sensitive features. When fixing paint in the oven, it is important to make sure that the fabric does not touch the oven heating element.