The Iron-Gall Ink Project

Iron-gall ink was the most common writing media for manuscripts from late classical times until the beginning of the 20th century. Its ubiquity is reflected in the manuscript collections of the Indiana Historical Society – the majority of which (in terms of collection numbers) are pre-1920.

The IHS Conservation Department is embarking on an iron gall ink treatment project to address problems inherent in the use of this ink.

The ink is chiefly composed of two ingredients whose interaction and resulting compounds can lead to long-range problems with preservation: Iron(II) sulphate and tannic acid. Corrosive effects caused by acid-catalyzed hydrolysis (sulphuric acid) and iron (II)-catalyzed oxidation of cellulose (excess iron(II) ions) can occur over time. Areas of paper covered with the ink can become brittle and fracture. In the worst cases, the paper breaks away in these areas leaving a lace-like remnant where writing once was.

Research into this phenomenon, of importance to collecting institutions throughout the world, began in earnest in the Netherlands in 1994. Since then, there have been three international conferences and dozens of articles in professional journals devoted to the topic. While preventative approaches such as proper storage conditions are important to a document’s longevity, it is clear that interventive treatment is also needed. Increasingly effective strategies to prevent or postpone iron-gall ink’s corrosive effects have now been developed.

The most up-to-date method for arresting the corrosive nature of iron-gall ink relies on a multi-step approach: 

• The selected manuscript item is first tested with an indicator paper to determine the presence of active iron(II) ions. It is the excess of this ionic state of iron which can lead to oxidation. A positive result leads to treatment.

• The item is washed as is normal with documents in the conservation lab. Attention is paid to solubility and fragility issues.

• After washing, immersion in an aqueous solution of calcium phytate chelates the free iron(II) ions. In this complex, they will no longer enter into oxidation reactions with cellulose.

• Deacidification of the document with an aqueous solution of calcium bicarbonate arrests the sulphuric acid-catalyzed hydrolysis of cellulose.

• Following these steps, the document will have tears repaired, wrinkles pressed and so on, as with other paper-based items in our collections.

The decision to test and treat manuscripts written in iron-gall ink is based on the desire to halt on-going degradation not sufficiently addressed in previous methods of treatment in the conservation field.