I take PFD and let it soak in soda ash until the liquid has all evaporated. What's left is as hard as a rock. The first time I thought I had ruined the fabric. But....since I didn't have anything to lose, I squirted dye onto it. And I loved the results!!
Here are two fat eighths after the SA has all evaporated. You can't tell it is quite hard by the photo so you'll just have to take my word for it (ORRRRR experiment with it on your own!!)
I used dye I had mixed for another project, let it batch. Washed it out and ironed it and VOILA!!
Great FIRE colors don't you think?