Here's one recipe you might enjoy trying. It's made from easy to find, nontoxic ingredients, and you'll feel like a medieval chemist as you brew it up.
1 black tea bag
1 ⁄3 c. charged full moon water
A small saucepan
1 ⁄4 c. white vinegar
1 unsoaped steel wool pad
Toothpick or wooden skewer
Optional: gum arabica; 3% hydrogen peroxide (both available at drug stores)
Place the tea bag in a teacup. Bring the full moon water to a boil; pour it over the tea bag and let steep for 15 minutes. Wring tea bag out and throw away. The tea now contains tannic acid.
In a small saucepan, warm the vinegar. Use scissors to snip bits of unsoaped steel wool into the hot vinegar, making sure the vinegar covers the steel wool. Heat until the steel wool dissolves and/or forms a colored solution (iron sulfate). Allow to cool.
Pour the tea into the small bowl. Use a piece of unbleached cotton to strain the iron solution into the tea. This will form black iron tannate. Be very careful: this is indelible and will stain whatever it touches.
Dip a toothpick or skewer into the "ink" and try writing with it. If it's too thick, thin the ink with a few drops of hydrogen peroxide. If the ink seems watery, let it sit out for a day or two until enough evaporates to make it slightly thicker. Alternately, add dabs of gum arabica to thicken the mixture.
Excerpted from Crafting Magick with Pen and Ink, by Susan Pesznecker