When printing white ink you must pretreat the shirt first. T-Print™ Pretreat Dark is designed to give white ink the base it needs on light and dark shirts for the print to jump off the garment! Make sure to follow the application directions on the container. For best results use a professional spray gun like the Wagner Power Spray. Too much pretreatment (soaking he shirt) can cause the print to not wash properly and the white ink to flake off.
Read and download the MSDS here.