Black walnuts are not the easiest nut to crack. Their hulls are tough and are not recommended for composting due to a chemical called juglone that is found in many parts of the black walnut tree. While juglone can be toxic to a few vegetables and plants, it isn't harmful to humans. What can be done with a difficult to crack shell? There are many beneficial uses for black walnut hulls, once they are cracked.
After the nut meat has been removed, the hulls (shells) of black walnuts are typically ground and sold for use in other products. The ground shells, called meal, is mostly used as an abrasive or a grit. This grit is sold as a tumbling abrasive in the jewelry industry and for polishing soft metals, plastics and fiberglass. Because black walnut shell grit does not break down easily it can be reused many times.
Further commercial applications find black walnut shells being used in the petroleum industry as an ingredient in maintaining seals (preventing oil from escaping). Shells are also used as a filtration product where the walnut shell assists in the separation of crude oil and water. In both instances the ground walnut shell is environmentally safe.
Referred to as an agrashell product, walnut shells are ground and used as ingredients in filler and adhesive products for plywood. Known as a blasting ingredient, black walnut shell is also used as an extender and a filler in dynamite. Cold casting methods use the shell mixed with resins. The shell is ground in various grades adhering to the needs of each product. Its size is referred to as a sieve size.
Body Care Industry
Once ground the shell has the ability to aid exfoliation, which makes it a desirable ingredient for the cosmetics industry. The ground black walnut shell is used in facial scrubs, body scrubs, foot scrubs and in soaps. Some dental abrasives also contain ground shells. Grit sizes tend toward a very tiny granule for denture polishing and slightly larger for smoothing the skin.
Black Walnut Dyes
Historically, black walnut has been used as part of the fabric dyeing process for centuries. Black walnut hulls help to produce the color black to a range of sepia tones due to the tannins it contains. Evidence of black walnut use is found in the remains of Pompeiian dyeworks and through the writings of Pliny The Edler, a naturalist and author from the first century.