c  2007 Institute of Chemistry, Slovak Academy of Sciences DOI: 10.2478/s11696-007-0053-0 Interactions in Iron Gall Inks V. JANČOVIČOVÁ*, M. ČEPPAN, B. HAVLÍNOVÁ, M. REHÁKOVÁ, and Z. JAKUBÍKOVÁ Department of Graphic Arts Technology and Applied Photochemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, SK-812 37 Bratislava e-mail: viera.jancovicova@stuba.sk Received 30 January 2007; Revised 12 April 2007; Accepted 16 April 2007 Dedicated to Professor Ľubomír Lapčík, DrSc., in honor of his 70th birthday Simple iron gall inks composed of gallic acid, ferrous sulfate, and gum arabic and in some cases also of copper(II) sulfate were prepared. The process of iron ion complex formation with gallic acid was investigated using UV-VIS spectroscopy, pH measurements, and by monitoring the concentration changes of Fe(II) ions. The admixture of Fe(II) ions to gallic acid induced a bathochromic shift of absorption bands at 215 nm and 265 nm in the UV-VIS spectra. Formation of a new absorbance band in the visible area was also observed and used to calculate the initial rate of complex formation. Concurrently, the pH values and the concentration of Fe(II) ions in the solution decreased. Gum arabic significantly enhanced the complex formation and its stability. On the contrary, the addition of Cu(II) ions to the solution decelerated the complex formation considerably. Keywords: gall ink, ferrous sulfate, copper(II) sulfate, complex formation, spectral properties INTRODUCTION The iron gall inks were one of the most impor- tant writing materials used to prepare documents, drawings, and other written materials from the an- cient times through the Middle Ages until the modern times [1, 2]. In Europe, they were used mostly from the beginning of the 11th century until the end of the 20th century. The libraries and archives all over the world contain an enormous amount of books (notes of Leonardo da Vinci), manuscripts, documents (US con- stitution proposal), and musical compositions (scores of J. S. Bach), which were written with iron gall inks. For preparation of iron gall inks, galls (from the chemical point of view these are polyphenols), vitriol (ferrous sulfate), gum arabic, and water, sometimes wine, beer, or vinegar as solvents, were used. Some- times pigments or copper(II) sulfate were added into these inks. The mixture of polyphenols with ferrous sulfate contained complexes which were in many cases darkly colored, while the black color was the result of their exposure to air [3—6]. Very low pH value of these inks presents a risk of damage to paper, a typical carrier material of hand-written documents. Chemical character of inks, especially their corrosive- ness, causes serious conservation problems. Damages include browning of the writing, paper breaking, holes in carriers, and the total loss of documents due to cor- rosion. One of the main reasons of corrosion of iron gall inks is the acid hydrolysis of the glycosidic bonds and the cellulose oxidation [7, 8]. In addition to acids, iron gall inks contain unreacted ions of iron. Research of the Middle Ages ink preparation recipes shows that the majority of historical inks contained exces- sive amounts of ferrous sulfate [9]. Ferrous ions react with peroxides produced during the oxidation of or- ganic materials (e.g. paper, cellulose) and highly re- active hydroxyl radicals are formed (Fenton reaction) [10]. Some organic compounds and peroxides can re- duce Fe(III) to Fe(II) ions which can again produce other hydroxyl radicals and cause degradation of cel- lulose. The component that can influence the reaction be- tween iron ions and phenolic acid is gum arabic, a binder used in the ink production. Rouchon Quillet *The author to whom the correspondence should be addressed. Chem. Pap. 61 (5) 391—397 (2007) 391