Dry black walnut powder can contain the nut's shell or hull depending on the powder's intended use. The most common black walnut powders contain ground shells and hulls. Powder made from the hulls is a potent natural dyestuff. It is also occasionally used for medicinal purposes, although, as Brian K. Hammons, president of the Hammons Product Company, points out, no one has yet linked specific health benefits to the product. Powder made from the black walnut shell enhances abrasive products used for cleaning and polishing in industrial and domestic settings. Hammons lists jet engines, musical instruments, ships and jewelry among the items cleaned with black walnut shell powder. Follow the guidelines below to make your own powder from black walnut hulls and shells.
Determine the intended use for your black walnut powder. If you want to make a walnut dye for textile and handmade paper dyeing, you will make the powder from the walnut hulls. If you intend to use your walnut powder for cleaning purposes, you will focus on the shells.
Peel the hull away from the shell. You will need to separate the shell and the hull, regardless of how you intend to use your powder. While the hulls are still green, peel them from the shell. To make hull powder, chop the peeled pieces as finely as possible and set aside.
Dry your chopped walnut hulls on fine mesh-bottomed racks. Spread a thin layer of hulls on each rack and store in a cool, dry place. Stir the hulls often to ensure even drying. Once your hulls have turned from green to dark black-brown and have a leathery texture, they are ready to grind.
Grind your dried hulls in a coffee grinder or blender that you do not intend to use for food preparation. Run your hulls through the grinder multiple times to create finer powders. You can finish your powder using a mortar and pestle. Choose a mortar with a rough interior texture to create a finer powder.
Grind your walnut shells. Black walnut shells are incredibly hard and do not break easily, so preparing a powder from shells is not always possible. If you want to attempt grinding your own black walnut powder, use a heavy-duty grinder. On the Missouri Department of Elementary and Secondary Education website, Calene Cooper suggests straining ground shells through a flour sifter to separate the powder from larger shell pieces.