Characterization of pigments and microclimate monitoring for the preservation of a rare medieval parchment

A rare medieval parchment called Exultet I preserved in the Diocesan museum of Metropolitan Capitolo of Bari has been studied. The Exultet was sung after a procession with the Paschal Candle before the beginning of the Liturgy of the Word in the XI century and it is certainly one of the highest literary and artistic expressions that Bari produced. Eight sheets with text, music lines and numerous beautiful miniatures painted upside-down respect to the liturgical text compose the parchment roll. The opening of the theca that preserves the unwrapped roll gave us the opportunity to perform diagnostic measurement on the pigments of the illuminated areas and to locate a wireless weather station for monitoring the microclimate. For these analyses a mobile laboratory has been set up in the museum. The techniques used for a non-invasive and in situ analysis of miniature paintings has been microscopic observation with digital microscope, UV-VIS-NiR spectrophotometry in reflectance mode with optic fibres (FORS), X-Ray fluorescence spectrometry (XRF) and finally μ-Rman spectroscopy. The use of several techniques is able to give us all information without causing any stress to the parchment especially if the measures are fast, as in our case (Aceto et al., 2012). The pigments have been identified mainly with FORS with comparison with standards and they are: red ochre and red lead used as red, lapis lazuli and azurite as blue, green earth and copper resinate as green, yellow ochre and orpiment as yellow. In the most important miniatures in some areas of the background, several traces of a residual gold leaf have been identified by XRF. The presence of rare and precious pigments as gold leaf and lapis lazuli underline the importance of the parchment. The preparation of the figures made by using a lead stylus has been also identified. The presence on all the roll of humpbacks formed in the last years well fit with the data collected that shows a continuity of condition between the showcase and the museum room. These means that the presence of visitors leads to changes in temperature, humidity and CO2, resulting much higher than those suggested for parchments. Finally the hypothesis of a repainting, formulated on the basis of the conservation status of the colours of the illuminated areas and from the comparison of similar hues, has been confirmed by the characterization of the colour palette. In some points the analysis returned the blue pigment as azurite and the red ones as minium, these results are in contrast with those of blue and red, respectively used, in all other illustrations of the roll were lapis lazuli and red ochre are plentiful.