I had a go at pre-mordanting a white cotton shirt from the op shop with iron water. The technique is explained in more detail in Gumnut Magic's e-book.
For this shirt I only used gum leaves which had been soaking in a bucket in the laundry for a couple of months.
The iron water pre-mordant combined with the soaked leaves have left gorgeous blue/black leaf prints.
You need to rinse off the soaking leaves before laying on the fabric or you end up with color splashing on to your fabric where you don't want it. Any sludge left on the leaves will also stop the colour from the leaves printing on to the fabric as I learnt the hands on way!
Blue is my favourite colour so I am very chuffed with this shirt!