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False- Infra Photography in the Identification of Pigments Used for a Late 13th Century Illuminated Manuscript

M.C. Buoso1, D. Ceccato1,2, D. Zafiropoulos1

1 INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy. 2 Dipartimento di Fisica, Università di Padova, Padova, Italy.

INTRODUCTION region. IR false color has been used as simple and inexpensive method for approximately determining The conservation and preservation of ancient artifacts is pigment identification in situ on painting or manuscripts. the main goal of cultural heritage investigators. Nowadays, the use of available non-invasive methods can provide information about materials, techniques and retouches due to previous restoration processes. Among other non destructive techniques (IR) reflectography and IR false- play an important role in diagnosis on artworks. The False-color , as a guide for identification of pigments, has been comprehensively investigated [1]. The method is extremely powerful and has proved its usefulness in the identification of a whole range of pigments. It also enables to differentiate between the different layers of painting applied using different methods at different times. The experimental procedure requires the combination of RGB color and IR reflectograms to create a false- color (or pseudo-) where each pigment is represented by a specific false-color that depends on its interaction with IR ; the interaction is strictly related to the chemical composition of the pigment and may also Fig. 1. Color sequence used for false-color image generation. depend on the painting technique used by the artist (i.e., color composition, and layers on the painted surface). An example of successful application of False-color The first experiences in Reflectography were carried out method to a 13th century illuminated Evangelistary, from with on infrared sensitive photographic films the Hellenic Institute of Byzantine and Post-Byzantine either - or color. Thanks to technological Studies in Venice, is presented. advances, such as the use of IR video and more recently CCD cameras, images of better quality and resolution were achieved. Moreover, the use of digital THE 13TH CENTURY EVANGELISTARY image handling programs has highly simplified the method. In the false-color image, information about the The parchment codex is composed of 414 measuring color in the RGB is discarded as only the red and 31.4 x 24.8 cm. The Gospel text is written in two columns components are combined with the IR component. In of 21 lines in a fine flowing Greek minuscule and clubbing detail, the red component in the RGB image is substituted Greek uncial. Part of the manuscript (MS) is in script with the IR, the green with the red, and the blue with the and ecphonetic notation in red while headings and small green (Figure 1). initials in gold over red. The script is minuscule and Areas with different color in the painting layer can be legible, appropriate for liturgical manuscripts. Each representative of the different pigments utilized in the passage starts with an initial letter, usually a T with artwork. Certain pigments, although differing in chemical ornamental motifs and an illustration relative to the composition chemical, have that appear similar to content. the eye. For instance, a very similar light blue color can be Miniatures have been painted to the right and left of the obtained by either the rare and expensive lapis lazuli or by text, in the margins, as well as between the two columns a much less expensive azurite. This means that they have and rarely, in the upper margin (Figure 2). similar absorbance spectra in visible light but they may An inscription with the name of Antonio Malakes, who highly differ in the IR absorbance. So similar colored lived in the 13° century, dates the manuscript in the second pigments may be identified by their absorbance in the IR half of the same century.

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Fig. 2. Example of historiated initial T and miniature from the examined artwork.

EXPERIMENTAL

The equipment used was a modified digital Sony DSC-W300 with capacity to record photographs in the Fig. 3. Identification of blue pigments used for the dresses and borders in miniature. infrared spectrum at a range > 750 nm. To capture the visible image, a IR blocking filter (X-NITE CC1) was applied and the images were recorded with an exposure time 1/13 seconds, aperture of 5.5. The pictures in IR light were recorded with a visible blocking filter (X- NITE 830) an exposure time of 1/25 seconds and an aperture of 5.5. The manuscript illumination was obtained using a standard fluorescent light, while infrared illumination was obtained using a RAYMAX High Performance Infra-Red LED illuminator. The visible and IR images were taken in the same geometrical condition and with the same camera setting. The white balance was manually set using a white sheet of paper. Several standard color charts (Kremer Pigmente) with pigment samples were taken in the same experimental condition. These color palettes were used to compare and identify, in an optical way, some of the constituents of the different colors used by the painter. The elaboration of the images was performed using a standard digital program. Fig. 4. Identification of red pigments used for , draperies and sandals of Christ. RESULTS AND DISCUSSION This is compatible with results of other studies [2]. The The investigation employed a simple in-situ false colour artist choice of pigments was consistent with the pigment photography. The same analytical technique were applied to several watercolor from Kremer range as the most artists of his era. A small number of pigments were consistently an One can conclude that the false-color technique provide conclusively identified; other pigments were identified less an good insight into the artist’s studio without damaging conclusively. The finding confirmed that a small range of the artwork. pigments was used: no more than one or two for each color group. From figures 2 and 3 the blue and red color obtained from different pigments are clearly identified. For the red madder lake and cinnabar were used while for [1] T. et al., Studies in Conservation, 37 (1992) 42-52. the blue hue ultramarine and . [2] L. Bugio et al. PNAS, 107 (2010) 5726.

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