Gelatine sizing and discoloration: A comparative study of optical spectra obtained from ancient and artificially aged modern papers Mauro Missori a , Marcofabio Righini b, * , Anne-Laurence Dupont c a Istituto Centrale per la Patologia del Libro, Ministero per i Beni e le Attivita ` Culturali, Via Milano, 76 – 00184 Roma, Italy b Istituto dei Sistemi Complessi, C.N.R. Sezione di Roma – Tor Vergata, Via del Fosso del Cavaliere, 100 – 00133 Roma, Italy c Centre de Recherches sur la Conservation des Documents Graphiques, CNRS 36 rue Geoffroy-saint-Hilaire, 75005 Paris, France Received 11 October 2005; received in revised form 2 February 2006; accepted 2 February 2006 Abstract The role of gelatine sizing in ancient paper discoloration is still subject to debate. In this report we have addressed this issue by com- paring the optical reflectance of sized and non-sized artificially aged modern papers with reflectance data obtained from a set of ancient specimens. We have used different ageing procedures and prepared the gelatine following methods set down in ancient recipes. Gelatine- sized aged papers showed an optical response comparable with that of ancient paper specimens, while very small reflectance modifica- tions were observed in pure cellulose unsized samples under the same ageing conditions. In addition, measurements carried out on pure gelatine films confirmed that gelatine plays a major role in paper discoloration. Some differences in discoloration effects induced by arti- ficial and natural ageing on sized paper are discussed and a possible explanation is proposed. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Ancient paper; Discoloration; Diffuse reflectance; Artificial ageing; Gelatine sizing 1. Introduction Research dedicated to the identification and optimization of procedures to be employed in paper conservation is con- centrated on acquiring a clear understanding of discolor- ation processes. Despite the fact that several studies have been presented that follow this line of enquiry [1–5], the complexity of the problem and the variety of possible approaches have made it difficult to obtain a complete pic- ture. Indeed, paper is, in general, a complex multi-compo- nent system consisting of a network of cellulose fibres, together with other substances, such as rosin, alum, glue, starch, dyes, pigments, gelatine and fillers, depending on the production technique employed. Moreover, the ageing sub-products of these substances can be found in the paper after a period of time, and these substances mostly depend on the environmental conditions to which it has been sub- jected [6,7]. However, up till now research on the ageing of ancient papers has largely ignored the role played by the siz- ing agent [8,9]. Early European handmade papers were mainly made from cellulose fibres and, to prevent the bleed- ing of inks, gelatine was used as size. Early papermakers saw additional advantages to gelatine including its ability to improve strength and the abrasion and soiling resistance of paper [10–13]. Gelatine is a protein obtained following the denaturation and structural degradation of collagen, the principal constituent of hard and soft connective tissue in animals [13,14]. In the past, these tissues were boiled in water (nowadays chemical treatments using acids or bases are used). Gelatine is the result of the somewhat random breakage of chemical bonds in collagen to form shorter chains of amino acids. The length of these peptide chains, which affects several properties of gelatine, can vary greatly depending on the preparation method employed [13,15]. The earliest use of gelatine as a sizing agent in replace- ment of the starch paste that was usually employed earlier 0030-4018/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2006.02.004 * Corresponding author. Tel.: +39 06 4993 4166; fax: +39 06 4993 4168. E-mail address: marcofabio.righini@isc.cnr.it (M. Righini). www.elsevier.com/locate/optcom Optics Communications 263 (2006) 289–294