Iron gall ink - Ingredients
Elmer Eusman (1998)
Iron gall ink is created from four primary ingredients: Tannin, vitriol (iron sulfate), gum Arabic and water. Different products were included in the recipes over time, but using these ingredients alone will produce a fine ink.
The term "tannin" has historically been used to describe a group of chemicals capable of tanning hides to make leather. There are different sources of tannin suitable for ink manufacture, but certain tree galls were known to contain a high concentration of this material. Galls are created by parasites which lay eggs in various types of vegetation. Several kinds of insects can cause the formation of galls, including aphids, flies and wasps. The female gall wasp, for example, punctures twigs on young oak trees to lay her eggs. The hatched larvae feed upon the tree, secreting an irritant that prompts the tree to create a growth around the larva. The gall provides both food and protection for the larva. After the larva has developed into a wasp, it chews its way out of the gall. Small holes in galls indicate where the insect has made its escape. Wasps that have not made it out can sometimes still be found inside the galls once cracked open. When the larva or insect is still inside the gall, the tannin content is said to be higher than if the insect has escaped.
There are many different types of galls (thousands!), all with varying tannin content. Aleppo galls (Aleppo is a province in Asiatic Turkey), acorn galls, oak-marble galls, Chinese galls and Japanese galls were used most often for ink manufacturing. (IMAGE) Tannin could also be extracted from other sources such as chestnut wood or bark, oak bark, the Sumach plant and pomegranate peels. However, these plant materials contain far less gallotannic acid. Gallotannic acid is the type of tannin most used for ink making and found in particularly high concentration in Aleppo galls.
It is the gallic acid groups in gallotannic acid that react with iron sulfate to create the colored ferric tannate complex. Hydrolysis of gallotannic acid can be accomplished by using acids or by letting the tannin solution ferment (leaving the solution exposed to air will rapidly result in mold growth on the surface), to produce gallic acid and water. Cooking in a slightly acidic solution, like wine, will also produce gallic acid.(See color formation: chemical reactions)
Vitriol is also referred to in recipe books as of copperas, sal martis, sulfate of iron, copper red, English vitriol, Roman vitriol, vitriolum cyprinum, and vitriolum hungaricum.
In Antiquity, vitriol was called chacantum ("blood of copper") by the Greeks and attramentum ("black" or "making black") by the Romans. The latter term was used both for the salt and for the color that it produced with tannin. Even more confusing is the close association between copper sulfate and iron sulfate. For centuries there was no distinction between these salts. Both products were obtained from minerals which contained many other metals, such as copper, aluminum, zinc and magnesium. Vitriol was contaminated in varying degrees with metals that do not contribute to color formation in an ink solution.
Vitriol was obtained from different mines and obtained by various techniques. In Goslar, Germany, a large concentration of natural vitriol supplied much of Middle Europe. Fluid was collected in large iron pans as it trickled out of the rock in mine shafts. Crystallized salts would form after the water had evaporated. The fluid was also collected in barrels, and vitriol crystals developed on a rope hung into the barrel as the fluid evaporated. To increase the iron sulfate content, scrap iron was added to the solution. Iron sulfate could also be obtained as a by product from alum manufacturing. The primary contaminant in this salt solution would be aluminum.
Gum Arabic is a vegetable gum obtained from the Acacia tree, native to Egypt and the Levant. The gum seeps out of the tree, forming globules sometimes as large as walnuts. It has an amber like appearance and varies in color from pale yellow to deep golden orange.
Gum Arabic is soluble in water. In an ink it functions as a suspension agent for the insoluble pigment particles. It also modifies the viscosity, and therefore the flow of the ink from the writing instrument. It binds the ink at the paper surface, producing a greater brilliance and deeper color. This binder was used very early in iron gall ink manufacture. As mentioned earlier, it was specified in a recipe by Capella, in the fifth century. Rarely are other binding agents, like egg white, mentioned.