It helps to use non-conducting ties and no salt. For really intense bright colors use the humidifying agent Urea. For really intense colors you can use more of the chemicals, more soda, more urea, more dye, in the same amount of water. Up to as much as double what we call for here. SODA 25 pounds UREA Amounts can vary considerably according to T-shirt weight, area dyed, and waste but this has been a useful rule of thumb.
Figure quantities proportionately for different numbers of shirts.
Use a pipet, syringe, brush, squeeze bottle, spray-bottle, spoon. Wear rubber gloves. This is the time the dye bonds to the fiber. Rinse until water runs clear. Yield will vary hugely, depending on coverage and intensity say, from 4 to 10 T-shirts.