The Iron Gall Ink Website

Conservation - Current methods

Robien van Gulik (1997)

The development of new treatment methods for iron gall ink corrosion represents a shift in focus within the conservation field. The emphasis of past treatment methods was on the physical stabilisation; whereas current methods aim to stabilize materials chemically. Previous methods improved the physical stability of an object in an effort to enhance its overall appearance. Contemporary standards for treatment require that the long-term preservation of the object is ensured as well. Methods currently used in paper conservation are listed below.



D eacidification methods are frequently used to inhibit ink corrosion. Deacidification will neutralize acids and therefore stops acid hydrolysis, one of the processes occurring during ink corrosion (Sistach, 1990). However, deacidification alone is not sufficient to stop ink corrosion completely. Acid hydrolysis is only one of the processes playing a role in corrosion by iron gall ink. The other degradation process involved is oxidation, catalyzed by iron in the shape of soluble iron-II ions (Banik, 1988). In addition to this, deacidification does not contribute to the strengthening of fragile papers. Certain deacidification solutions, like calcium bicarbonate and magnesium bicarbonate, have so-called "buffer capacity". They can stop acid hydrolysis also in future, but only when sufficient surplus is added to the paper ("alkaline reserve"). 

Deacidification agents can be categorized as aqueous and non-aqueous. Well known aqueous agents are calcium hydroxide, calcium bicarbonate and magnesium bicarbonate. Among the non-aqueous deacidifying agents are barium hydroxide in methanol, magnesium oxide ("Bookkeeper"), magnesium titanium ethoxide ("Battelle") and methoxy magnesium methyl carbonate, ethoxy magnesium ethyl carbonate, magnesium methyl carbonate and magnesium ethyl carbonate (all four of them "Wei T'O" solutions). The aqueous agents present problems in the area of bleeding and washing out; the non-aqueous agents in the area of penetration, effectiveness and solvent retention. Recent research shows yellowing of paper (Bukowsky, 1997) and browning of inks (Neevel, personal communication) when magnesium compounds were used. This effect can possibly be attributed to the high pH reached by magnesium compounds (Green, 1991; Krekel 1997).


Boiling water

Manuscripts corroded by iron gall ink can be immersed in boiling water, protected by a Hollytex envelope (Heller, 1993; Biggs, 1997). This treatment is used frequently in Germany, Italy, Norway and Switzerland. During this process 50 - 100% of the destructive (soluble iron-II) ions are removed from the paper, as well as acids. Rag paper appeared much stronger and more flexible after treatment (Heller, 1993; Biggs, 1997). No bleeding or discoloration of the ink was seen (Biggs, 1997). Some papers, however, might shrink by this treatment, possibly depending on the paper and the drying conditions. (Reißland, personal communication). Furthermore, increase in temperature causes acceleration of chemical reactions.



Treatment of manuscripts by splitting the paper and inserting a new stable core between the two layers of paper is a technique developed in Jena and Leipzig, Germany (Müller 1989; Wächter 1997) and widely used. A facing paper is glued to the document on both sides with gelatine. This is dried under pressure and when dry, the facing papers are split, thus splitting the inserted document neatly in two layers. A deacidifying agent can be added to the new core, which is attached with starch paste. When the starch is dry, the sandwich is put into a bath containing protease to dissolve the gelatine so the facing papers can be removed. The gelatine used for splitting possesses, like all proteins, mild complexing properties, thus it is able to bind a certain amount of soluble iron-II-ions. Acids are also partially removed by this technique because of the moisture in the gelatine and the enzyme bath at the end of the process. This is one of the few treatments which, besides taking away part of the iron and acids, effectively reinforces the fragile paper degraded by ink corrosion. The technique can presently be carried out almost completely by machine (Wächter, 1997).


Non-treatment, treatment of symptoms

Non-treatment consists usually of strict climatological control and an acid free environment. Research on the ideal environment to slow down ink corrosion as much as possible, is being carried out in Delft (TNO). Treatment of the symptoms of ink corrosion like silking, lining and local repairs can be added to this. Non-treatment has the advantage of neither using insufficient treatment for iron gall ink corrosion, nor any treatment that is insufficiently examined for side effects and aging.