For centuries, much of the world's knowledge was preserved and transmitted through the magic of oak gall ink. The swellings on the oak tree--natural reactions to the attacks of parasites--were collected and ground up with additional materials to produce an important writing substance. Oak gall ink is waterproof and grows darker with age. It bites into the paper, like a kind of acid, making the text virtually indestructible. Yet it can be prepared by almost anyone and, in fact, was. Everyone, from medieval monks to Early American schoolchildren, mixed preparations of the West's most common form of ink.
Collecting and Preparing Oak Galls
Oak galls look like small, brown balls, similar to nuts but more spherical in appearance. They can be found attached to the branches of oak trees. To prepare oak gall ink, you will need to collect a number of these oak galls. The oak galls are surprising light. Each one contains fibers that are rich in gallotannic acid. When combined with water, gallotannic acid becomes tannic acid. Tannic acid is best known for its traditional use in transforming raw hides into leather. This same astringent property is the secret of oak gall ink.
To make your oak gall ink, you must first prepare and collect the natural tannic acid. Smash or crush a bunch of oak galls and place them in a pot of water. Ideally, you will want to use a rusty old iron pot. Iron is absolutely necessary to the reaction that releases the tannic acid. Soak the oak galls in an iron pot for 3 days. Transfer the contents to a larger pot with an additional quart of water. Place over a heat source and simmer until at most half of the liquid evaporates. Let cool, and then drain through a coffee filter or cheesecloth.
Alternatively, if you do not have an iron pot, you can simply cover the oak galls with boiling water. While the water is cooling, soak a handful of iron nails in vinegar. The vinegar will rust the iron and become completely discolored. When the boiled oak galls have cooled, drain them through a coffee filter or cheesecloth; you want only the liquid. Combine this liquid with the liquid from the rusty nails.
Preparing the Ink
The liquid you have prepared can be used for writing as is, but it will be very light in appearance, and possibly somewhat difficult to read. Medieval monks often burned parchment to make fine ash. They added this ash to the liquid mixture to make a darker ink. You can try burning paper or just simply adding a small quantity of dye.
Add a binding agent to your ink to keep the component parts from separating out in the solution. Traditionally, gum arabic is added to the mixture. Store your ink in a sealed container, and do not make too much at one time, since it is best used within a few weeks. Even with the addition of the binding agent, oak gall ink eventually goes bad. It will gradually darken and become unusable.