|One of the main issues with coloured clothing in general as well as airbrushed clothing is the washability.|
The paint I use is specifically made for fabric and comes with its own instructions for its use. However modern washing machines and powders can take there toll, and if that doesn't get it the tumble drier will.
Once the shirt is painted by us, we use a heat press to set the paint into the fabric, at this point it is waterproof, water by its self will not move it, but start applying a bit of heat and you soften the paint whether thats in a washing machine or a tumble drier.
So look after your t-shirt after all it is the only one like it in the world!