Sooo ... I made my first batch of walnut ink today (Christopher's recipe from this thread, since it seemed so easy) and here's what I learned, maybe it's of help to some of you:
Make lots: I only had 4 or 5 husks and that's definitely not enough. It's supposed to cook for an hour at least, and if you have only a few husks, the amount of water you put in the pot evaporates very quickly. Next time I'll definitely put in more husks and therefore more water, so that there's enough left even if half of it evaporates. I had to put in more water several times, which isn't really the point I think. The logical conclusion is that my ink is very light. I'll leave it open for a while and see if it darkens.
It does write very smoothly though. Not *quite* as well as the one I bought, but my hand slipped when pouring in the gum arabic, so there's probably too much in there.