In order to make the ink, you need to collect from an underside of oak leaves yellow "nuts" and putting them in a metal jar, fill it with water. After some time, add a solution of iron sulphate. It may take a few hours - and ink ready.
"Nuts" with oak leaf (leaf galls)
Great ink work of planed oak bark. It is boiled in water (about 15-20 minutes). When the liquid becomes dark brown color, it is filtered and pour the solution of iron sulphate (so the ink was black) or chloride, iron (ink will turn dark blue).
Where were invented ink?