Any walnuts will work with this recipe, from tiny native Arizona walnuts to big, fat English walnuts, which are the kind you buy in stores. But you do need them hull and all, so this only works if you have a tree nearby. The pickling liquid in my recipe is very traditional; you'll see variations on it throughout England. I've also made a Chinese-inspired version with Sichuan peppercorns and star anise replacing the allspice. This recipe makes about 3 quarts.
Dissolve the salt in the water to make a brine. Put on some rubber gloves if you have them, because walnut juice will stain your hands for weeks -- and it won't come off. Trust me on this one. Properly gloved, stab each walnut with a fork in several places; this helps the brine penetrate. Submerge the walnuts in the brine and let them ferment for 8 days at room temperature.
Remove the walnuts and put them on a baking sheet and leave them outside in the sun for a day, until they turn uniformly black. You can do this step without gloves if you want.
Pack the walnuts into quart jars. Bring the remaining ingredients to a boil and pour over the walnuts. Leave very little headspace in the jars. Seal and keep in a cool place, either the fridge or a basement -- you just want them to rest below 70°F -- for at least a month before you eat them. Kept this way they will last a year.
Note that prep time does not include fermenting time.