Iron Gall Ink
© Copyright 2002 by Lois Fruen
This article accompanies the textbook The Real World of Chemistry 6th ed by Lois Fruen Kendall/Hunt Publishing ISBN 0-7872-9677-5
Iron-gall ink was the most important ink in Western history. Leonardo da Vinci wrote his notes using iron-gall ink. Bach composed with it. Rembrandt and Van Gogh drew with it. The Constitution of the United States was drafted with it (Ink Corrosion). And, when the black ink on the Dead Sea Scrolls was analyzed using a cyclotron at the Davis campus of the University of California, it was found to be iron-gall ink (Nir-el 157).
Some ancient scrolls were written in carbon ink. Carbon inks were the first writing inks. They were used as early as 2500 BC. These inks were made by burning oil or tar to produce soot, which contained about 80% carbon. The carbon was mixed with water and gum in a suspension. The problem with carbon ink was that it smudged (Eusman 3). The red ink on the Dead Sea Scrolls is cinnabar (HgS) (Nir-el 97).
Pliny the Elder (23-79 AD) wrote in his histories that galls were used to produce dyes. He described an experiment that he did using a piece of papyrus that he dipped in gallic acid. He noted that when he dripped a solution of iron salt onto the papyrus, it turned black (Eusman 3).
To make iron-gall ink, galls from oak trees were crushed to obtain gallotannic acid. The gallotanic acid was mixed with water. As seen in Figure 1, the water breaks the ester links of the gallotannic acid, forming gallic acid (Sjostrom 101).
Figure 1: Water breaks the ester links of the gallotannic acid, forming gallic acid
The gallic acid was then mixed with water and vitriol (iron (II) sulfate). Gum arabic from acacia trees was added as the suspension agent (Eusman 1). The result was iron-gall ink.
gallic acid + FeSO4.7H2O + water iron-gall ink
When modern scientists used spectrometry or infrared spectrometry to analyze samples of iron-gall ink from various ancient scrolls, they determined that the ink samples were either ferric gallic acid complexes or iron pyrogallol complexes (Eusman 7).
The inks on parchment and paper can also be analyzed using photon induced X-ray emission (PIXE). PIXE can be used without sacrificing any material. The X-ray beam is aimed at the spot to be analyzed and excites the inner shell electrons. As the electrons return to ground state, they emit characteristic X-rays specific to the elements that are present. Iron-gall ink is identified by the high levels of iron (Lambert 100).
Iron-gall ink was very useful because it did not rub off documents. Unlike paper, parchment was not absorbent, so carbon-based ink easily rubbed away. Iron-gall ink ate into the parchment by reacting with collagen in the parchment. Iron-gall ink also reacts with cellulose in paper or papyrus, which poses a problem for modern conservators, especially when the ink has eaten all the way though a document. Some ancient documents written with iron-gall ink have holes where the ink was applied. Some of these texts can still be read by "reading the holes" while others have been destroyed (Nicholson).
Research has shown that the high acidity of some inks and excess iron (II) sulfate are the culprits. To conserve documents that were written with iron-gall ink, the documents must be deacidified and the excess iron (II) compound removed or converted to a less harmful compound (Banik 2).
"An Introduction to Parchment: Inks." Public Record Office Preservation. 14 Jul. 1998. www.pro.gov.uk/preservation/parchhist.htm.
Banik, Gerhard. "Ink Corrosion." Stuttgart: Staatliche Akademie. 5 Nov. 1999.
Eusman, Elmer. "Iron Gall Ink." Paper Conservation Department. Rotterdam. 5 Nov. 1999. www.knaw.nl/ecpa/ink/html/make.html.
Koren, Zvi. "HistoricoChemical Analysis of Plant Dyestuff Used in Textiles from Ancient Israel." Archaeological Chemistry: Organic, Inorganic, and Biochemical. Washington DC: American Chemical Society, 1996.
"Ink Analysis By an Early Model Cyclotron." Time Magazine. 10 Mar. 1986.
"Ink Corrosion." Paper Conservation Department. Rotterdam. 5 Nov. 1999. www.knaw.nl/ecpa/ink/html/make.html.
Karmes, Cyntia (sic). "How to Make Iron-Gall Ink. Paper Conservation." Paper Conservation Department. Rotterdam. 5 Nov. 1999. www.knaw.nl/ecpa/ink/html/make.html.
Nir-el Y. and M. Broshi. "The Black Ink of the Dead Sea Scrolls." Dead Sea Discoveries. Mar. 1996: 157-167.
Sjostrom, Eero. Wood Chemistry: Fundamentals and Applications. Orlando: Academic Press, 1981.