Here is a picture of some wovens that I stained.
I etch them first and then let them soak in strong coffee for about 24 hours. I do still need to wipe any excess off in some spots and they also can't get wet right away. As time goes on, the stainging becomes more permanent, but I don't have any real detailed research on how long though.
I have also baked them in the oven at about 250 degrees in a puddle coffee before, but I like the look of the longer soaking better.
Serena