From the net, since we don't pickle walnuts here in the U.S. Sounds interesting though...
Ingredients:
Green Walnuts
1/2 cup salt for every 5 cups water (for brine)
For spiced vinegar:
For every 5 cups white vinegar, add 2 tablespoons peppercorns, 2 walnut-sized pieces 0f dried gingerroot and 2 tablespoons whole allspice.
Directions:
For the Brine:
Boil the water and pour in the salt. Stir well to dissolve and cool before using.
Wearing rubber gloves, prick the walnuts all over with a thin skewer or metal knitting needle. Put them into a bowl and cover with brine. Put a plate on top of the walnuts to keep them under the surface and leave 5-6 days in a cool place. Drain, cover again with fresh brine and leave for another week. Drain well, spread on a tray and leave in a warm room or, better still in the sun. Turn them occasionally and leave for 2-3 days or until they turn black.
For the spiced vinegar:
Crunch the spices lightly to bruise them, tie in a piece of cheesecloth and add to the vinegar. Boil in a covered enamel or stainless steel pan for 10 minutes. Cool and remove the spices.
Pack walnuts in dry jars, then cover with spiced vinegar, seal at once and leave 7-8 weeks before using