I found a walnut tree last weekend. These green walnuts are just about right for pickling. Green walnuts should still be soft inside with no shell formed yet. You can test this by poking it with a needle and making sure there is no shell.
The process of pickling walnuts is fairly long. Make sure you wear gloves! Walnuts will stain your hands and clothing with a strong black dye! Wash and trim the walnuts then soak them in brine for a week.
At first they will be a nice green colour but....
After a few days in the brine you can see the black dye starting to become apparent. Walnut juice was used in days gone by as an ink from which many illuminated manuscripts were drawn. More updates later.