The black walnut has a long history of being used to produce a dark stain that can be used as ink, leather making dye, wood and grass stain and textile dye. It’s lightfast, colorfast and doesn’t respond to most solvents, so difficult to get out in general. Scrapbookers now also use walnut ink to give paper an antique look.
To make the ink you will need unhulled walnuts, water, a pot (it helps if it is rusty cast iron as the iron deepens the color), a sieve or cheesecloth and a stirrer. Some people also add rusty metal to the mix to darken the color and vinegar to help preserve the liquid.
Here is Annamarie Malik making a large batch of ink:
She sells bottles of walnut ink from her website http://annamalik.com/