So, seeing as how ink is currently a scarce commodity in the game, and you can only find it in fest shops and from treasure chests, I think this should be able to be crafted. Here's a suggestion of how it could be made with current IG items and processes. These techniques are very similar to how ink is currently made.

ITEMS:
foraged something, such as a flower, nut, fruit, or vine
oil from a crushed herb or flower
a piece of iron, as ingot or nugget form

TECHNIQUE:
Boil iron and foraged item together, until all that is left is unfinished ink and a piece of iron. (Boiling would reduce the quality, then eventually would boil away)
Combine the oil and ink mixture, and shake in a container. Let sit for an amount of time to cure.

RECIPE SUGGESTION:
3 parts water to 1 part foraged item, which makes 1 volume of unfinished ink.
4 volumes of unfinished ink to 1 volume of oil, to make 5 volumes of finished ink.