Image of CBL Syc 706: Detail of damage caused by severe iron gall ink corrosion.

Conservation Book Club: Iron Gall Ink

20 November, 2020

This week’s #ConservationBookClub blog post focuses on the topic of iron gall ink.

Iron gall ink was used as a writing ink and drawing medium up until the start of the 20th century and is commonly found in manuscript collections throughout the world, including those here at the Chester Beatty. It was often favoured over carbon ink due to ease of manufacturing and indelibility once applied to a substrate, making it ideal for record keeping. When made well, the ink is permanent and stable, however there are many instances of a complex degradation process resulting in what is known as ‘ink corrosion,’ where the ink burns through the substrate.

The issues of iron gall ink degradation and various conservation methods have been studied extensively by conservators and scientists, but each treatment comes with its own limitations—there is no one size fits all solution. Understanding the chemical process of degradation and having an awareness of treatment options allows for informed decision making, which can guide conservation planning. Given the complexity of this subject, there are many, many articles available on iron gall ink and its conservation. For this reason, I have made a list containing some of the articles and resources I have found to be particularly useful.

To make it easier to navigate the list is split into two groups; part one (references 2-6) focus on the identification, chemical composition and condition assessment of iron gall ink; Part two (references 7-16) on conservation treatments. I hope you’ll find something relevant to your own work below.

Screenshot of the Iron Gall Ink Website homepage.

1. Iron Gall Ink Website

The Heritage Cultural Agency of the Netherlands runs the Iron Gall Ink Website, which contains a wealth of information on iron gall ink. From manufacturing and historic recipes, to web tutorials on the corrosion process and risk factors, to a discussion of non-interventive and interventive conservation treatments! This website is incredibly thorough, and definitely worth checking out.

Understanding iron gall ink: identification, chemical composition and condition assessment

Although there are many different historic recipes for iron gall ink, the primary ingredients are tannin—often extracted from oak galls (see photos below)—iron sulphate, gum and water or wine. The quality and ratio of ingredients determines the stability of the ink, however the amount of ink applied, composition and finishing of the paper or parchment substrate (e.g. thickness, sizing etc.), and exposure to moisture are also factors.

The two main causes of iron gall ink corrosion are acid hydrolysis due to an excess of sulphuric acid and the iron (II)-catalysed oxidation of cellulose. Both reactions are catalysed by water.

Image of Oak galls caused by the Oak Marble Gall Wasp, (left) on the oak tree, and (right) with emerging wasps. Thanks to Kristine’s mum for these pictures.
Oak galls caused by the Oak Marble Gall Wasp, (left) on the oak tree, and (right) with emerging wasps. Thanks to Kristine’s mum for these pictures.

2. Birgit Reißland and Judith Hofenk de Graaff, Condition rating for paper object with iron-gall ink

This information sheet by Birgit Reißland and Judith Hofenk de Graaff is a useful tool for conservators to refer to as it contains a visual assessment form and condition rating system for iron gall ink corroded papers. It gives a clear and concise description of the chemical process and four stages of iron gall ink degradation and includes simple diagrams and photos to help the reader visualise the process. I would also recommend reading the four articles listed as references at the end for further information, by Birgit Reißland, Gerhard Banik, and Cathleen A. Baker.

Made available by the Heritage Cultural Agency of the Netherlands, ICN-information number 1, 2001.

3. Ewa Bulska and Barbara Wagner, "A study of ancient manuscripts exposed to iron-gall ink corrosion"

This paper in the 2004 volume, Non-Destructive Microanalysis of Cultural Heritage Materials,
discusses the use of modern analytical techniques to investigate the structural and chemical properties of paper samples from historic manuscripts endangered by iron gall ink corrosion. They authors also made their own model samples and used these for initial tests evaluating the potential to extract non-bound iron ions from the ink.

Chapter 17, Non-Destructive Micro-Analysis of Cultural Heritage Materials , K. Janssens and R.van Grieken, Elsevier, Dordrecht, The Netherlands, 2004.

Images of CBL Syc 706 (Syriac, 14th or 15th century): Details of damage caused by severe iron gall ink corrosion.
CBL Syc 706 (Syriac, 14th or 15th century): Details of damage caused by severe iron gall ink corrosion.

4. Johan G. Neevel and Birgit Reißland, “Bathophenanthroline Indicator Paper Development of a New Test for Iron Ions”

Now frequently used to help identify iron gall ink and check the effectiveness of potential treatments (and the risk of iron (II) ions migrating), Bathophenanthroline indicator paper was first developed by Neevel and Reißland. This article provides a thorough introduction for its practical use in paper conservation. A non-bleeding indicator paper, it turns magenta when in direct contact with ink containing iron (II) ions, though further tests are needed to identify iron (III) ions. Neeval also published a further article Neevel, Johan G., “Application Issues of the Bathophenanthroline Test for Iron(II) Ions” in 2009.

PapierRestaurierung, Vol 6, No 1, 2005, pp 28-36.

5. Díaz Hidalgo et al, “New insights into iron-gall inks through the use of historically accurate reconstructions”

Published in 2008, this Heritage Science research article is made freely available by Springer Open. It discusses the preparation of medieval inks, reconstruction of five historical recipes from the Iberian Peninsula and analyses the composition of the inks produced.

Heritage Science volume 6, Article number: 63, 2018.

Image of an Iron gall ink drawing in CBL Cpt 813 (Pauline Epistles & Gospel of John, c.600).
Iron gall ink drawing in CBL Cpt 813 (Pauline Epistles & Gospel of John, c.600).

6. Joanna Kosek and Caroline Barry, “Investigating the condition of iron gall ink drawings: developing an assessment survey”

This recent article looks specifically at the impact of iron gall ink damage on Western iron gall ink drawings, rather than manuscript collections. It discusses collection management, risk-assessment protocols, ink corrosion models, and develops condition assessment ratings through surveys of the collection.

Journal of the Institute of Conservation, Volume 42, 2019 – Issue 3, pp.191-209.

Conservation treatments: chemical and mechanical stabilisation

Over the last 30 years there has been a great deal of research to find the best way to treat iron gall ink corrosion. However, the format of the object, specific ink composition, extent of damage, type of substrate and many more factors can differ from one object to the next meaning any potential conservation treatment has to be individually tailored.

Of these treatments, phytates—particularly the ‘calcium phytate’ treatment—have emerged as the most widely accepted method among conservators. Although proven to be effective, this is an aqueous treatment, making it highly interventive and problematic to use on material that is bound or contains highly soluble inks or other media. As most of the collection we work on at the Chester Beatty is original manuscript material, phytate treatments would generally be considered too interventive (e.g. CBL Syc 706, which has severe iron gall ink damage but a historic binding structure and soluble red and green inks). However, there is continuing research to improve and adapt phytate treatments and come up with new chemical solutions to treat iron gall ink corrosion even in these challenging circumstances.

To treat the mechanical damage caused by iron gall ink, a repair method is needed which limits the amount of moisture introduced to the object. For this reason, remoistenable tissues are one of the most commonly used repair techniques for repairs on moisture sensitive objects. These can be pre-prepared with a range of adhesives, such as isinglass, gelatine and methylcellulose, with Japanese tissues of varying weights. Transparency, adhesive strength and flexibility are key considerations as well as the activation method: water, water + solvent, or solvents alone.

Images of CBL Is 1522 (Maghrebi Qur'an, 16th or 17th century)
CBL Is 1522 (Maghrebi Qur'an, 16th or 17th century)

7. J.G. Neeval, “The Development of a New Conservation Treatment for Ink Corrosion, based on the Natural Anti-Oxidant Phytate”

The pioneer of the phytate treatment, Neeval published the first article discussing the potential of phytates to treat iron gall ink corrosion on paper in the 1990s. The ability of calcium phytate to reduce further corrosion caused by iron gall ink is now widely accepted in the conservation world and phytates have become a commonly used treatment method. Although there are limitations on what material it can be used on, since it is an aqueous treatment, and the method has been refined since this article was published, it is still an important read.

Restaurator, 1995, 16, pp.143-160.

8. Jana Kolar et al, “Stabilisation of Iron Gall Ink: Aqueous Treatment with Magnesium Phytate”

A study that aims to demonstrates that magnesium phytate is equally as effective as calcium phytate for treating iron gall ink and inhibiting corrosion. They even suggest that it may be more advantageous.

e-Preservation Science, Vol 4, 2007, pp.19-24.

9. Claire Dekle and Mary Elizabeth Haude, “Iron-Gall Ink Treatment at the Library of Congress: Old Manuscripts, New Tools”

The Library of Congress has extensively researched treatments for iron gall ink as the medium has been used in a significant proportion of their collection. This 2008 article uses the findings of scientific research into iron gall ink corrosion completed at the Library of Congress to create new treatment protocols and develop a unified approach to the conservation of paper-based collections containing iron-gall ink. It introduces a methodology to guide treatment decision making and give cases studies to demonstrate how these tools can be used in practice.

The Book and Paper Group Annual 27 (2008) pp.15-26.

To access more of these guidelines/forms see, Sylvia Albro et al., “Developing Guidelines for Iron-Gall Ink Treatment at the Library of Congress,” The Book and Paper Group Annual 27 (2008) pp.129-165.

Image of Iron gall ink damage and abrasion in CBL W 217 (Franciscan Antiphonary, Italy, 15th century).
Iron gall ink damage and abrasion in CBL W 217 (Franciscan Antiphonary, Italy, 15th century).

10. Patricia Engel and Gayane Eliazyan, “Treatment of ink corrosion in a bound book - Armenian manuscripts of the Matenadaran Collection in Yerevan”

Available as a free PDF on Academia, this article describes a potential solution for in situ application of aqueous solutions. The authors suggest the use of a suction manuscript wedge to limit the spread of aqueous solutions and potential tidelines and enable localised treatment of iron gall ink corroded areas in a bound volume. They then successfully apply this method to an iron gall ink damaged Armenian manuscript.

Available from the authors via

11. Sherry Guilda, Season Tsea and Maria Trojan-Bedynskib, “Technical Note on Treatment Options for Iron Gall Ink on Paper with a Focus on Calcium Phytate”

A brief but useful technical note for conservators, providing a practical guide for treating works on paper with iron gall ink. It summarises treatment options depending on the solubility of the ink and highlights possible treatment steps.

ACCR, vol. 37, 2012, pp.17-21.

12. Véronique Rouchon et al, “Methods of Aqueous Treatments: The Last Resort for Badly Damaged Iron Gall Ink”

Discusses methods of safely using the calcium phytate treatment to manuscripts badly damaged by iron gall ink. Through testing on samples and then original manuscript material, the authors investigate how to minimise the mechanical risk of applying a water based solvent system to paper in poor conditions, for example float washing rather than immersion.

Journal of Paper Conservation, IADA, 2012, 13 (3), pp.7-13.

13. Oulfa Belhadj et al, “The Dutch Fe-Migration Mending Test”

The Dutch Fe- Migration Mending test allows conservators to test aqueous treatment methods for iron gall ink and assess the degree of ink and iron ion migrations around the original ink line. Proposed treatments can be applied to a paper impregnated with bathophenathroline and stamped with iron gall ink. Then migrations of Fe (II) out of the ink line are visually assessed through the occurrence of pink halos. The authors evaluated several different treatments using this method, revealing that this test is not suitable for evaluating all alcohol and water-based treatments but that it is particularly useful for assessing humidification.

Journal of Paper Conservation, Vol. 15, 2014, No. 1, pp.9-15.

Image of Iron gall ink damage (left) and remoistenable tissue repairs being applied (right) in CBL Is 1404 Qur’an folio (Yemen or Syria, early 8th century).
Iron gall ink damage (left) and remoistenable tissue repairs being applied (right) in CBL Is 1404 Qur’an folio (Yemen or Syria, early 8th century).

14. Eliza Jacobi, Birgit Reissland, Claire Phan Tan Luu, Bas van Velzen and Frank Ligterink “Rendering the Invisible Visible - Preventing Solvent-Induced Migration During Local Repairs on Iron Gall Ink”

Eliza Jacobi, “Moisture and mending: A method for doing local repairs on iron-gall ink”

Two key articles by Eliza Jacobi et al. directly inform current conservation practice for the treatment of objects with iron gall ink. Keeping in mind that excessive exposure to water causes ink migration, and the movement of damaging iron II ions, the authors investigate a variety of adhesives and application methods to repair iron gall ink corrosion. Through testing, they demonstrate how the use of remoistenable tissues, together with bathophenanthroline indicator paper, can provide the best results for local mending of iron gall ink-corroded areas.

Journal of Paper Conservation Vol. 12 (2011), No. 2.

Adapt & Evolve 2015: East Asian Materials and Techniques in Western Conservation. Proceedings from the International Conference of the Icon Book & Paper Group, London 8–10 April 2015 (London, The Institute of Conservation: 2017), pp.80–90.

Images of Iron gall ink damage and remoistenable tissue repairs being applied to CBL W 136 (Crete, 1577/8).
Iron gall ink damage and remoistenable tissue repairs being applied to CBL W 136 (Crete, 1577/8).

15. Andrea Pataki-Hundt and Cosima Walter, “Comparison of lightweight Japanese tissues for overall stabilization of documents damaged by iron gall ink corrosion and an alternative to silkscreen frames”

This article focuses on the mechanical, rather than chemical, stabilisation of severely damaged iron gall ink documents. The authors suggest a practical workflow, including using a different support when completing aqueous treatments on fragile objects; compare a range of thin Japanese papers in terms of visibility; and discuss lining versus local repair when treating severe corrosion. I have found this to be a useful article to refer to when considering repair materials and methods.

Restaurator, International Journal for the Preservation of Library and Archival Material, 2018, 39, pp.109-127.

16. L. Völkel, T. Prohaska and A. Potthast, “Combining phytate treatment and nanocellulose stabilization for mitigating iron gall ink damage in historic papers”

This Heritage Science paper has been made freely available by the authors on ResearchGate. It evaluates the use of nanocellulose to stabilise mechanical damage from iron gall ink.
The study aims to integrate application of the nanocellulose into a multi-stage calcium phytate/calcium hydrogen carbonate treatment, which combines deacidification and stabilisation. The suitability and stability of two types of nanocellulose applied to paper damaged by iron gall ink are evaluated in detail. Nanocellulose is still a relatively new material so more research is needed to fully understand its different applications for paper repair, but it is clear it has a great deal of potential for use in paper conservation.

Heritage Science volume 8, Article number 86, 2020.


We would love to hear about the articles you find most useful, so please get in touch with us over on Instagram.

Sophie Coulthard, Conservation Intern 2019/20

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