This is how sun printing on fabric works:
1. After the fabric has had all the sizing etc. washed out of it I lay it out flat in the sun.
2. Then I mix up the dye, in this picture it looks like I am using Setacolor, but I also use Jacquard "Dye-na-flo" either are good. Jacquard has a lot more colors to choose from and the colors remain more true when mixed with water. Ooo-look at the farmer tan!
5. When it is dry (patience-fiddling with it can ruin it) the stencils are removed and viola! Everywhere it was masked off from the sun it has turned white. Now it just needs to sit for 24 hours and then be heat set with an iron or clothes dryer.