I make this! (I got into making dyes for all natural tie-dye shirts) It's cool and relatively easy, but it will eat your paper. It's a cool novelty, but not for anything you want to store long term.
Interesting about it being destructive to the paper - the Wikipedia article seemed to describe old manuscripts lasting a long time with the ink. Is it that the paper we have now is less compatible? I'm guessing you might also be into paper, since you're into ink. Do you collect your own galls? The main reason I found iron gall ink fascinating, was that the ink is described as being common and widespread, but made fro…
The article describes how the oxidation, which causes the ink to darken, causes a reaction between tannic acid and these newly created ferric ions. Doesn't that neutralise the acidity? If so, perhaps it is a case of 'survivorship bias' in the old manuscripts which do survive, as they had just the right ratio of tannic acid to iron ions to completely neutralise, whereas the books written with ink containing not enough iron ions would be damaged and discarded.