Oak gall ink, or iron gall ink, is one of the oldest ink types we have: it’s been found on papyruses from the first century after Christ; one of the earliest and most complete manuscripts of the Bible — Codex Sinaiticus — was written using this ink; and I’ve been told Leonardo da Vinci used it, too. Iron gall ink has been in common use up until very recently.
The ink is produced using oak galls. An oak gall is an outgrowth we can find on oak trees, and is a result of a wasp laying its eggs in the tree. When the hatched wasp larvae starts feeding on the tree, it creates an irritation which results in the formation of the oak gall, and this oak gall encompasses the larvae. Eventually, when the larvae has become a wasp, the young insect makes a hole in the gall and leaves.
To create ink we take this gall, dry it, pulverize it, and soak it for some time in distilled water. Then we filter the liquid and we mix the results with ferrous sulfate (known since ancient times as copperas or green vitriol). As soon as the ferrous sulfate is added to the oak gall “juice,” the liquid changes from dark brown to blueish black. It’s pure magic! It’s then best to mix in some gum arabic, to thicken the ink and make it stick better to the paper.
Be warned: the iron in this ink could be corrosive, leading to what we call ink corrosion, which is when the ink — over time — eats it’s way through the paper. That, to say the least, is not ideal for archival purposes. However, many old documents written with this ink seems to survive quite well, so apparently a lot of scribes throughout history got their recipe ratios just right.
