Find straight twig about size of pencil, and whittle point at one end. Dip pointed end into walnut ink (recipe below) and print letters. If point becomes flat or soft, simply sharpen point again.
8 whole walnut shells
1 cup water
1/2 teaspoon vinegar
1/2 teaspoon salt
Put shells between pieces of heavy cloth, and hit with hammer to break into small pieces.
Place broken shells and water in saucepan, and bring water to boil. Simmer on low heat for a half hour or until water changes to dark brown color.
After mixture cools, pour through strainer or paper towel into cup. Stir in vinegar to prevent color from fading and salt to keep ink from turning moldy. Pour into small jar, and screw on lid for storage.
Try making ink with bark, roots, berries, or other nut shells.