Board Thread:Off Topic/@comment-25857155-20151110093941/@comment-25396609-20151119005308

Google-fu netted me this:

Use 1/2 cup fresh berries or thawed frozen berries; push them through a strainer so that you get pulp-free juice. Add 1/2 teaspoon of vinegar (to hold color) and 1/2 teaspoon salt (as a preservative) and mix well. You can use a glass baby food jar as your 'inkwell', if you have one. Walnut Ink.