I don’t know how or why this idea came to my mind. But I got my shirt, and taped off what I didn’t want dyed.
Then, using an empty (and cleaned) spice shaker I sprinkled the dye powder mixed with salt onto the dry shirt. And sprayed it lightly with a mixture of warm water and vinegar, and let it dry.
Once it was dry I shook off as much as I could and removed the tape, sandwiched it between 2 old towels and washed it.
Aside from the fact that the stripes turned out purple instead of black it is exactly how I pictured it. I will be making more shirts using this technique.!