[bigattichouse]

You can add a little calcium carbonate to these inks to give them a little shine and offset some of the acidity.

The really neat thing about these inks is that they are soluble when made, and you can write on a document, then - as they dry - , the soluble iron tannates that work into the fibers form an Fe3+ tannate, which is insoluble - you aren't writing on the surface, you're dying the fibers. This is why palimpsest can occur when documents where scraped and re-used (so you can read the originals with Xray methods)

Source: I have a battery patent based on iron-gall inks (US10749168B1), and it's fun stuff to play with! (see more @ http://bigattichouse.com )