Take about 1/2 cup of ripe berries, of whatever kind you want, and crush them through a strainer over a bowl. When they are completely crushed, add 1/2 tsp. vinegar and a 1/2 tsp. salt. The type of berry you pick determines the color of the ink. The vinegar ensures that the color will hold, and the salt acts as a preservative. Store small amounts of this ink in a tightly sealed container, or the ink will go bad.
Crush between 10 and 15 walnut shells and put them into a saucepan. Cover them with water and simmer them for 30 minutes. Remove them from the stove and let them soak overnight. After the soaking, strain out the shells and add 1/4 tsp. of vinegar to make the color hold. Store this ink in a tightly sealed container.