In the early days of manuscript production both carbon and iron gall inks were used for their rich, dark black color. Carbon ink, however, fell out of common use around the 12th century. The carbon based ink, often times was gritty and could be effortlessly wiped from the page. It was iron gall that remained the most routinely used ink well into the 19th century, due to it’s ability to soak into the page more efficiently, leaving a lasting mark, not easily removed.
There is no single recipe for iron gall ink. However, there is good record of the seemingly endless ways to create the mixture. While medieval scribes and illuminators might have disagreed on the nuances of creating the ink, possibly due simply to the tradition of the monastery, but also because of the availability of some materials in certain areas, there are ingredients that are found in nearly all the recipes: a form of sulfate, gum, and oak gall.
The most interesting of these three commonly used ingredients would most likely be the oak gall. These apple-like tumors grow on the twigs of many species of oak tree, after certain varieties of Cynipidae, a particular family of gall wasp, lay their eggs in newly forming leaf buds. After a larvae begins to grow, the tree has a reaction to the intruder. This retort from the tree creates the oak gall, also known as an oak apple. And it is with that strange tumor-like growth that the ink is made. The sulfate is added to transform the ink from a brown to a deep black. While the gum is used to suspend the mixture.
Cited below is an English translation of a 15th century French recipe for the ink:
Observe that choice and tried writing must be made in this way. Take 3 ounces of galls, the goodness of which may be known by their being wrinkled. Take an equal quantity of gum arabic, the goodness of which may be known by its being bright and easily broken, and the smallest is the best. Take 3 1⁄2 oz. of Roman vitriol [sulfate copper], the goodness of which may be known by its being a blue color, and solid, and coarse after the manner of coarse salt. Afterwards, take four pounds, of twelve ounces to the pound, of clear water, which if it is rain water, or water from a cistern in which rain water is kept, is better than well, spring or river water; and put it into a new metal or glazed earthen jar, which has never been used for anything else, in order that it may be pure and clean from all filth; and into this water, put the galls roughly pounded so that each grain of gall may be broken into four or five pieces, and then let the galls boil in the water without gum or vitriol, until the water is reduced to one-half. Then let it be strained through a cloth or piece of linen, and be put back without the substance of the galls in the vase over there, and let it remain there until it begins to boil, and then put into it the gum ground and pulverized, and let it boil gently for a short time, namely, until the gum is dissolved. Having done this, pour into it directly two pounds of the best pure and white wine, and stir it a little, and then immediately add the vitriol well pulverized, stir it again a little, and then remove the vase from there, and mix the whole together in order that the vitriol may be well incorporated with the galls, and the gum, and the water. Having done all these things in order, put the vase with the ink in the open air, and let it stand for one night, in order that the air make it brilliant and more black. And therefore if it be done in fine weather, it will be better and finer. Afterwards, strain it through a cloth, and put it by, and keep it for use.
Also included is a video depicting the ink being made using a different recipe, however the main three ingredients remain the same. Details on the recipe used in the video are in the video's description on youtube.com.