The few times I shelled them (and ended up giving most of them away because I couldn't eat them all myself), I used these directions from the University of Minnesota:

Harvest
As black walnuts ripen, the husk changes from solid green to yellowish green. Walnut juice leaves a dark stain, so wear gloves or use tongs when you handle unhusked walnuts. Press on the skin of the walnut with your thumb; ripe nuts will show an indentation. Weekly monitoring is important as nuts will mature over a four to six week period. Try to harvest the ripe nuts directly from the tree, ahead of the squirrels. If the nuts are too difficult to reach, they can be collected after they fall from the tree during frosts. Often the husk of mature nuts has dried and cracked. Husks must be removed before you store black walnuts.

Prepare for Storage
Removing the husk is an important step in storing black walnuts properly. If the nuts are stored with husks attached, the heat released as the husks decompose will discolor walnut kernels and ruin their flavor.

Hulling walnuts, removing the husk, can be a difficult and messy task. The indelible dye from the husk stains hands, clothes, tools and work surfaces. If you are working with dry nuts, the husk can be removed by applying pressure to the ends of the nut. This can be done by pounding side to side with a hammer, of course while wearing safety glasses.

The husks can also be softened in a container filled with a slurry of three parts nuts to one part water and a handful of gravel. Stir the mixture vigorously. It may take more than one attempt to completely remove the husks.

If you are hulling a large quantity of nuts, the slurry can be used in a small portable cement mixer. An old-fashioned corn sheller will also be useful in hulling black walnuts.

Take care when hulling or shelling walnuts. The practice of driving over nuts with an automobile can be a dangerous one. Nuts and broken shells may be thrown into the air by the tires, possibly causing bodily injury or property damage.

After hulling, wash the unshelled nuts. Black walnut shells can also leave stains, so rinsing walnuts outside with a garden hose may be the best idea.

Kernel quality can be affected by insects such as walnut weevils and husk fly maggots; darker than usual husks may be evidence of insect damage. Check for insect feeding by placing the nuts in a bucket of water. Nuts without injury will sink; discard any nuts that float.

When cleaning up after hulling black walnuts, it is best to place leavings in the trash. Do not compost walnut husks. Juglone, a naturally occurring chemical released by all parts of black walnut trees, can have a toxic effect on many vegetables and landscape plants.

Curing
After husks have been removed, the nuts must be cured. Curing prepares the walnuts for storage and allows the walnut flavor to develop. To cure black walnuts, stack the clean hulled nuts in shallow layers only two or three nuts deep. Place the nuts in a cool, dry, well-ventilated area out of direct sunlight for two weeks.

To be certain nuts have cured adequately, break open a sample nut. When the nut is dry enough to store, its kernel will break crisply, with a sharp snap. If cured improperly, nuts will mold.

Storage
After curing, store unshelled nuts in a well-ventilated area at 60°F or less. Cloth bags or wire baskets allow adequate air circulation and discourage development of mold. Try to keep the relative humidity fairly high, ideally about 70%. Nut shells will crack and the kernels spoil if nuts are stored in too dry an area.

When you're ready to shell the nuts, moisten them to keep the kernels from shattering. Soak the walnuts in hot tap water for about 24 hours. Drain and replace the hot water and soak the nuts for two more hours. Cover the nuts with moist cloths until you're ready to crack the shells.

After shelling, nut meats can be stored in several ways: at room temperature, refrigerated or frozen. If you plan to store the nutmeats in a container at room temperature and use them within a few weeks, first bake them at 215° for 10 to 15 minutes. Nutmeats can be refrigerated in a jar or plastic bag for up to nine months without baking. Nutmeats can also be frozen for longer term storage, but use them within two years.

Preparing black walnuts for baking involves several steps: harvest, hulling, curing, cracking and storage. Many people, however, find the time and effort well worth it.

Black walnuts are very hard to crack and I wouldn't attempt it with a standard nutcracker. I used c-clamps that I already had to crack the nuts (A c-clamp is a metal clamp in the shape of a "c". A large one costs $10-$15 at a hardware store.) . I started out using a small one in the 3 inch range but it was rendered unusable before I was done. So I had to switch to a larger one to finish. The larger one worked better and it was easier to use. I wasn't getting halves but I almost always got quarters. (I didn't soak them before cracking, it would have certainly been easier)

One other thing I found out is that there isn't much nutmeat inside of them. I had about 4 pounds of black walnuts in-shell and when I cracked them I only got 14 ounces of shelled nuts. I had a grocery bag of shells and only a little over half a quart bag of nutmeats. They taste great and they are free but they take a lot of work. I'll have to gather a lot more next year.

Rodney

Tasty, but a lot of work to pick the bits of nut out of the labyrinthine shells.

But the hardest part is to get the meat out. BW is much tastier and flavorful than other walnuts.