Stabilisation of iron gall ink containing paper

The anti- and pro-oxidative properties of gallic acid in the presence of Fe(III) were evaluated. The experiments were performed at several different pH values of the reaction solutions, and at several different temperatures. Gallic acid was shown to have pro-oxidative properties as iron chelator and antioxidative properties as hydroxyl radical scavenger; in excess of Fe(III), the antioxidative properties prevail. The results are useful in conservation chemistry for optimisation of conservation procedures, and in medicinal and nutrition chemistry for the evaluation of the role of polyphenolic antoxidants in food and human body, especially after consumption of polyphenol-rich nutrition, such as wine, tea or fruit.

The study aiming at the evaluation of the variables, which result in poor condition of some documents, but excellent of others shows, that the most important factors, which are influencing the degradation of historical documents are the width of the ink line, which is correlated with the absolute amount of ink applied to the paper, pH of the area containing the ink and paper grammature. The regression model employed is able to describe more than 50% of the total variance in the L* values, which indicates the extent of degradation caused by the ink corrosion. Additional variance may be partly ascribed to factors, which we were not able to evaluate, but which have significant effect on the paper degradation, most notably environmental influences on the documents during the centuries of their storage. Based on the result of the study, it is now possible to predict the stability of historical documents containing iron gall ink by determining the three critical factors- grammature of paper, width of ink lines and pH of the paper containing the ink. The result is therefore useful for evaluation of a condition of the collection written with iron gall ink and thus allows for preservation planning and best use of resources.

Besides iron, other transition metals like copper can be present in historical iron gall inks. Like iron ion, copper ion catalyses the oxidative degradation of cellulose, thereby hampering the permanence of paper artefacts. It is therefore imperative to detect its presence in inks, dyes and pigments. A facile non-bleeding indicators test using 2-(5-nitro-2-pyridylazo)-1-naphtol has been developed to enable identification of the presence of copper ions in conservation workshops. The non-bleeding test for copper fulfils most requirements: it is non-destructive, easy to apply and sensitive enough to detect copper in iron gall inks on originals. While 40% of conservators were able to identify the presence of copper, when its concentration was 10ppm, as determined by PIXE, all conservators identified the presence of copper in the inks, when its concentration exceeded 26ppm.

The contribution from Institute Jozef Stefan (IJS) to the InkCor project is based on the use of Ion Beam Analytical (IBA) techniques running at the recently implemented tandem accelerator - TANDETRON. Here, the Proton Induced X-ray Emission (PIXE) method, due to its non-destructive nature, high sensitivity and high rate of data accumulation, is essential for the study of historical documents. The extensive database on elemental concentrations in inks and papers, originating from measurements of statistically well proved number of documents (more than 800 measuring points), has been formed this way. The data serve as the basis for scientific decision for possible conservation treatments, and are at free disposal to partners collaborating within the InkCor project. Besides, the experimental techniques developed are of innovative character and can be disseminated and applied by scientific community through the international exchange of scientific data.

Novel conservation treatments for stabilisation of paper's oxidative decay were evaluated by an interdisciplinary group consisting of chemists, physicists, conservators and art historians. A number of instrumental techniques were used, such as size exclusion chromatography and viscometry, UV/VIS spectroscopy, FTIR, and PIXE. Model iron gall ink was prepared and applied uniformly to model gelatine-sized rag paper. Full Arrhenius study was performed at temperatures between 60 and 90 degrees Celsium in order to obtain stability data at close to ambient conditions. Photo-stability of samples was also evaluated. The evaluated prototype treatments will be further developed by the participating SME into a first commercially available product for non-aqueous stabilisation of ink corrosion. This is expected to contribute to development best preservation strategies for corroded documents and have a considerable economic impact for the SME. By enabling the preservation of the artefacts, the results will have an impact on the sector of cultural tourism in Europe. The results will be extensively disseminated to conservators and decision-makers via workshops (2 already organised), exhibitions (3 organised so far) and publications.

A simple monkey proof method to identify iron gall ink is of the utmost importance. Ink corrosion can be very disastrous for object of cultural value made out of paper. It is essential that object of cultural value are as complete as possible, especially in the case of an archive witch have not only historical and cultural value but, sometimes also legal value. The simple method for iron and copper- tests, as developed and optimised in this project, has been proven to be very helpful for conservators, enabling them to identify the ink on the objects. Especially in comparing to inks that didnt contain iron or copper but look very similar to iron gall inks. This is very important in order to make a conservation plan that is suitable for the objects and (part) of the collection.

XRF analysis of historical inks show iron as the most important metal with most common concentrations between 0,25 - 0,27mmol/g. In the majority (85%) of the inks, copper content was below the detection limit of the method 0,008mmol/g. SEM-analysis showed that Fe, Na, K and Ca were present in all inks at least as traces. S, Al, Si, Mg and Cl were present in nearly all manuscripts. In order to detect the source for the high potassium contents of the inks, gall-nuts and gum arabic of several provenances were analysed as well. Potassium was indeed always present, sometimes also Ca, Al and Mg. The results are useful for the development of novel conservation solutions.

The catalytic effect of transition metal ions, i.e. Fe(III), Cu(II), Co(II), Cr(III), Cd(II), Zn(II), Ni(II) and Mn(II) in reaction systems containing hydrogen peroxide and hydroxyl radical scavenger was evaluated at different pH and temperature. The rate of hydroxylation was followed using spectrophotometry and from this rate, the rate of production of hydroxyl radicals was estimated. This rate was shown to correlate with the corrosiveness of metals in paper. The result can be used in studies of the behaviour of transition metals in similar reaction systems, e.g. in nutrition, polymers, or the human body.

In addition to non-aqueous processed, the development of which was the key objective of InkCor project, one aqueous process is extensively used by the conservation community. Existing aqueous stabilisation process was evaluated and improved. This is expected to contribute to development of best preservation strategies for corroded documents. By enabling the preservation of the artefacts, the results will have an impact on the sector of cultural tourism in Europe. The results will be extensively disseminated to conservators and decision-makers via workshops, exhibitions and publications.

Historical text sources containing information on writing materials and writing tools in general were collected. They contain recipes for iron gall inks in Arabic, Dutch, English, French, German, Greek, Italian, Latin and Spanish language from the 3rd century AD to the early 20th century. Around 90 title descriptions and ca. 250 iron-gall ink recipes from the collected historical sources were entered into the ArTeS database (ArTeS = Art Technological Sources) owned by the ICN. The inks were reconstructed in the following way. 19 selection criteria were defined and applied to about 150 of the iron-gall ink recipes entered into the ArTeS database. Looking for common denominators applicable to the objectives of further workpackages of the InkCor project, it was found that about 20 % of the searched recipes had equal proportions of "galls" and "vitriol" in common. About 5% of the searched recipes had alkaline ingredients or presumable anti-oxidant suppliers in common. Based on the historical recipes, 23 inks were prepared for reconstruction purposes.

In an attempt to develop a non-aqueous stabilisation treatment for ink corroded documents composed of alkali and antioxidants, the possible stabilising potential of some non-aqueous mass deacidification solutions on a model paper containing model iron gall ink were evaluated. All deacidification methods resulted in increased stability of iron gall ink containing paper, as demonstrated by a higher bursting strength and DP of ink containing paper after dynamic ageing experiment. However, it appears that a slightly better effect may be achieved with the processes using magnesium titanium ethoxide than magnesium oxide. This behaviour is probably due to the fact that the alkali (magnesium titanium ethoxide) in the former is dissolved in the organic solvent, leading to a more uniform distribution of alkali throughout the paper after deacidification than in case of magnesium oxide, in which case we have a suspension of MgO in non-aqueous solvent.

Databases in MS Access and Filemaker Pro have been developed for the visual assessment and documentation of historical documents and drawings corroded by aggressive inks. They contain scanned images, accompanied by a detailed description by conservators. The objects are rated into four damage categories. The databases will enable conservators to evaluate the ink corroded documents and drawings in their collections in a reliable way. For the Teyler Museum, the Filemaker Pro database is an important tool in accessing detailed information about the inks used in drawings in the museum's collection.

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