In a small glass jar, submerge steel wool in 150mL vinegar. Soak in the sun for 24 hours.
The next day, drain and set aside. Boil 150 mL of water for a few minutes. Add 2 teabags and steep for 5 minutes. Then boil the tea and bags. Strain and add 45mL (3Tbsp) of tea to the vinegar mixture. It will turn a purplish black.
Write or draw with it on less absorbent paper or illustration board. Arches 140lb hot or cold press work well. It will at first appear faint, but will slowly turn to a darker sepia as the iron oxidizes. You’ll have some tea left. I poured mine over the steel wool to get a little more ink. The color of this ink seems to change less. Before you're ready to draw, add 1-3 teaspoons of binder to the ink. Ideally this would be gum arabic. PVA glue will due in a pinch, such as Tacky Glue or Elmer's.
The Science of Ink Making Iron Gall inks have been in use from the medieval period to the present day. They were important for commerce and correspondence. Governments even provided standard recipes for civil servants. It is the chemical reaction of Iron (II) Sulphate and tannic acid that causes the immediate change in color when the new compound ferrotannate combines with oxygen in the water. As the ink dries its color darkens as it oxidizes.
The ink, when not properly made, can be very unstable. Apparently a 3:1 ratio of acid to iron produces the most stable ink. Our recipe is certainly deficient in this regard. Iron sulphate is present as an impurity in steel wool, and additional sulphur is found in the vinegar, which besides removing the protective oxidation from the steel wool, also is able to increase the iron sulphate content of the solution. The tea is used as a source of tannins, but other sources could also be used, such as oak leaves, black walnuts, or oak galls. Additional recipes can be found at this link.