Black walnut ink
Walnut ink is an ink made from the green husk surrounding the nut of walnuts, commonly the Juglans Nigra walnut is used. It can be made domestically or is widely available online. The ink, dye or pigment may be liquid or made of crystals that are mixed with water before use. It can also be used for all forms of dyeing and for the creation of a very dark natural ink.
Black walnut ink was made by artists de Onkruidenier during their residency at the Jan van Eyck Academie.