Determination of the Fe(II)/Fe(III) ratio in iron gall inks by potentiometry: a preliminary study

Cédric Burgaud (1, 2) , Véronique Rouchon (1, 2) , Alain Wattiaux (3) , Jean Bleton (4) , René Sabot (2) , Philippe Refait (2)

1 CRCC - Centre de Recherche pour la Conservation des Collections
2 LEMMA - Laboratoire d'Etude des Matériaux en Milieux Agressifs
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
4 LETIAM - Laboratoire d'Etudes des Techniques et Instruments d'Analyse Moleculaire

Ancient iron gall ink manuscripts can be treated by immersion in water to dissolve excess iron compounds known to be involved in the degradation of such manuscripts. In this study, redox potential measurements were performed so as to follow the dissolution of iron gall inks from original degraded manuscripts over a period of time. Due to the complexity of the system, potentiometry was also applied to understand the interactions between the main components of iron gall inks, namely Fe(II) and Fe(III) sulphates, gallic acid and gum arabic. All these components were electrochemically active but the redox potential was mainly governed by the Fe(III)/Fe(II) redox couple. It could be demonstrated that one gallic acid molecule could readily reduce, in the experimental conditions considered here, up to four Fe(III) cations.

Mots clés: Potentiometry; Gallic acid; Fe(II)/Fe(III) redox system; Ancient manuscripts

Domaines: Matériaux

Cédric Burgaud, Véronique Rouchon, Alain Wattiaux, Jean Bleton, René Sabot, et al.. Determination of the Fe(II)/Fe(III) ratio in iron gall inks by potentiometry: a preliminary study. Journal of electroanalytical chemistry and interfacial electrochemistry, 2010, 650 (1), pp.16-23. ⟨10.1016/j.jelechem.2010.09.015⟩. ⟨hal-00547209⟩