Can't you just buy tannic acid from somewhere? Every tea will stain the paper whereas you'll get much cleaner paper base and highlights with plain tannic acid... And, definitely clear very thoroughly (develop, then clear in mild citric or acetic acid for instance...)! If not, you'll again get muddy / stained highlights and low contrast.
You should lbe able to get tannic acid in wine making shops. I've got some, but I've only successfully toned one or two prints. As soon as we start getting some warm sprintime sun, I'll try some fresh prints... this thread is sparking my interest in cyanotypes again.
Tom, on Point Pelee, Canada
Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...