Cristina Cicero et al.: Thermographic analysis of hidden text and illuminated manuscripts

In recent years active infrared thermography (IRT) has been successfully applied to the study of a large variety of cultural heritage items. Thanks to its non-destructive nature and its capability to be used in situ, this technique proved to be a good tool for the investigation of small artefacts Analysing the heat diffusion process induced within the sample by artificial thermal stimulations makes it possible to obtain information on the surface and subsurface structure of the artefacts detecting opto-thermal inhomogeneities .[1-2]. In this paper we report on two recent thermographic applications to library materials concerning the analysis of written scraps buried in bookbindings and of illuminations.

From the 16th century, mainly due to the invention of printing and the consequent increase in the book production, it became very common to reuse earlier library materials. From then on until the 20th century when the preservation of cultural heritage started to be taken more seriously, printed or manuscript sheets of paper and parchment were normally used to reinforce the boards of new bindings or for the lining of the book [3]. From codicological and palaeographical points of view, the identification of such hidden features of bookbinding becomes an important issue, and the possibility of detecting and reading these buried texts, provides a unique opportunity to ascertain the existence of a codex now destroyed.

We will present some results obtained by the application of active IRT to a series of books from the Bibliotheca Angelica of Rome. Thanks to the IRT investigations, many written scraps located beneath the end papers could be detected and analysed in a completely non-invasive way, without disassembling the book. With this method, the light coming from lamps penetrates the end paper and reaches its opposite surface where it is locally absorbed by the ink of the buried text which gets selectively warmed up. The IR radiation emitted by the warmed ink is recorded by an IR camera that generates an image (thermogram) of the buried text, clearly readable. [4]

This technique has also been used in order to investigate structural defects and inhomogeneity in illuminations. In the paper we report on the results obtained by the thermal analysis of 313 illuminated letters of a 15th century antiphonary from the Biblioteca Angelica of Rome, which was performed on the occasion of its restoration. The analysis enabled us to detect and characterise detachments of the gildings, inhomogeneity of the parchment support and underpaintings. In particular, the presence of detachments of the gold leaf from the underlying layers has been tested on every illumination. Due to a specific consolidation treatment, the air gaps have been filled and the detachments are no longer detectable confirming the effectiveness of the adopted method [5].

The authors would like to thank Fiammetta Terlizzi and Mirella Fidomanzo, Biblioteca Angelica di Roma, for providing the investigated samples.

References:

[1] Mercuri, F., Zammit, U., Orazi, N., Paoloni, S., Marinelli, M., Scudieri, F.: Active infrared thermography applied to the investigation of art and historic artefacts. Journal of Thermal Analysis and Calorimetry, 104, 2 (2011): 475-485.

[2] Mercuri, F., Orazi, N., Zammit, U., Paoloni, S., Marinelli, M., Valentini, P.P.: Thermographic analysis of cultural heritage: recent applications and perspectives. e-PS, 9 (2012): 84-89.

[3] Caldelli, E.: I frammenti della Biblioteca Vallicelliana. Studio metodologico sulla catalogazione dei frammenti di codici medievali e sul fenomeno del loro riuso. Roma 2012.

[4] Mercuri, F., Gnoli, R., Paoloni, S., Orazi, N., Zammit, U., Cicero, C., Marinelli, M., Scudieri, F., Hidden text detection by Infrared Thermography. Restaurator, 34, 3 (2013): 195-211.

[5] Orazi, N., Mercuri, F., Cicero, C., Doni, G., Paoloni, S., Zammit, U., Marinelli, M., Analisi termografica delle miniature di un antifonario del XV sec. In: Atti del IX congresso nazionale IGIIC-Lo Stato dell’Arte, Accademia Delle Belle Arti di Bologna, Bologna 10-12 Ottobre 2013.

Authors:

C. Cicero, F. Mercuri, N. Orazi, U. Zammit, S. Paoloni, M. Marinelli, Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata". Rome.