High Street Copper Oxide Ink
You don't have to be a mad scientist to have copper around, but it doesn't hurt to know one! Just kidding. Scrap copper can be found in all kinds of places. I often have a stash of copper wire and blanks in a discard pile from jewelry-making. Once brewed over a few weeks' time, copper oxide ink is a beautiful aqua that tends to separate into liquid and crystals (do not handle the crystals with bare hands). Great for drawing, abstract art, and just playing around.
Found in New Hampshire.
High Street Copper Oxide ink made with: copper, salt, vinegar.
Shake before using; store in cool dry place. Some natural inks fade over time and with exposure to light.
Warnings: TOXIC! Not for human consumption