Yesterday I gave the umbrella a good soaking. I used the shower head to pound it with both cold and warm water. I then left it to sit in some water for a while before letting it dry out.
All the prints weathered the treatment well. Both the stazon solvent ink and the acrylic / enamel ink print were just as vibrant after the water test as before. However, the fabric paint print was ever so slightly faded. I am sure this is because it was not heat set properly.
So I am clear in my recommendation - acrylic or enamel ink! Both maintained vibrancy and were easy to use. Just use sparingly. So I am off to buy some more in different colours to finish off this umbrella for Amelie.