I've been having fun! I've been dying (pun intended) to do this for ages! You just mix up dye and pour it down the fabric. I don't have a place I can do messy things so this is my carport.
And my work bench!
The dye has to cure for at least 4 hours and not dry out in that time. I didn't want to ruin the streaky effect and hadn't thought about how to cure it until after I had dyed the fabric. Fortunately I bought a plastic drop cloth on a roll and had the brilliant idea (no modesty here!) of putting out a length of drop cloth and laying the fabric carefully on top, then covering with the drop cloth. I left the fabric until it stopped dripping so that the dye stayed put. Hopefully it will still look good tomorrow morning when I wash it out.