Medieval manuscripts are made with a blue-black ink to which tannins are no stranger: from the Middle Ages to the 19th century, our inks were prepared with tannin!
Let us begin by recalling the love affair between tannins and metals: tannins, in fact, bind to metals, including iron. This is the reason for the bad taste of red wine drunk with a fish dish: tannins, which are abundant in red wine, carry iron during the winemaking process. This iron reacts with the unsaturated fatty acids found in abundance in fish, releasing compounds that taste unpleasant! There are two solutions. You can drink white wine, which is less rich in tannins and therefore iron. Alternatively, drink red wine with fish low in unsaturated fatty acids, such as tuna-this way the unpleasant compounds are not detected.
The binding of metals to tannins often changes the color of the tannins: in the past, dyers used iron or aluminum to dull the colors of plant tannins used to dye textiles (we will devote a future column article to this). You may have noticed the blackening of chestnut wood, which is rich in tannins, when it comes in contact with nails in facades or fences. In fact, tannins often blacken in the presence of iron: this was used to make historic inks–and here is the recipe.
A tannin-rich plant raw material, such as bark or oak wood, is needed. The best way is to use oak galls. These outgrowths are produced by small insects, the chinipids, which lay their eggs in the buds and turn them into woody protuberances where the larvae, or oak galls, grow. The tree has tried, in vain, to defend itself against the attacker by accumulating tannins that account for 50 percent of the gall’s weight!
To create a historical ink, then take the plant raw material: bark, wood, or ideally gall. Crush it coarsely, then add water and boil it for a long time in an old pot (which you then cannot wash!). Then add iron sulfate (50g/L) or, alternatively, soak a rusty nail at the end of the boiling. Cool for a long time and filter through a very fine mesh cloth before using this viscous liquid to load the pen to avoid clogging it. Now you have a medieval ink, the ancestor of industrial dyes, a beautiful dark purple that later turns blue-black.