False-Color Infra Red Photography in the Identification of Pigments Used

for a Late 13th

Century Illuminated Manuscript

M.C. Buoso1, D. Ceccato

1,2, D. Zafiropoulos

1

1 INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy.

2 Dipartimento di Fisica, Universit di Padova, Padova, Italy.

INTRODUCTION

The conservation and preservation of ancient artifacts is

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 Infrared (IR)

reflectography and IR false-color photography play an

important role in diagnosis on artworks.

The False-color infrared photography, 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 images and IR reflectograms to create a false-

color image (or pseudo-color image) where each pigment

is represented by a specific false-color that depends on its

interaction with IR light; the interaction is strictly related

to the chemical composition of the pigment and may also

depend on the painting technique used by the artist (i.e.,

color composition, and layers on the painted surface).

The first experiences in Reflectography were carried out

with photographs on infrared sensitive photographic films

either black-white or color. Thanks to technological

advances, such as the use of IR video cameras and more

recently CCD cameras, images of better quality and

resolution were achieved. Moreover, the use of digital

image handling programs has highly simplified the

method. In the false-color image, information about the

blue color in the RGB is discarded as only the red and

green components are combined with the IR component. In

detail, the red component in the RGB image is substituted

with the IR, the green with the red, and the blue with the

green (Figure 1).

Areas with different color in the painting layer can be

representative of the different pigments utilized in the

artwork. Certain pigments, although differing in chemical

composition chemical, have colors that appear similar to

the eye. For instance, a very similar light blue color can be

obtained by either the rare and expensive lapis lazuli or by

a much less expensive azurite. This means that they have

similar absorbance spectra in visible light but they may

highly differ in the IR absorbance. So similar colored

pigments may be identified by their absorbance in the IR

region. IR false color has been used as simple and

inexpensive method for approximately determining

pigment identification in situ on painting or manuscripts.

Fig. 1. Color sequence used for false-color image generation.

An example of successful application of False-color

method to a 13th

century illuminated Evangelistary, from

the Hellenic Institute of Byzantine and Post-Byzantine

Studies in Venice, is presented.

THE 13TH

CENTURY EVANGELISTARY

The parchment codex is composed of 414 measuring

31.4 x 24.8 cm. The Gospel text is written in two columns

of 21 lines in a fine flowing Greek minuscule and clubbing

Greek uncial. Part of the manuscript (MS) is in gold script

and ecphonetic notation in red while headings and small

initials in gold over red. The script is minuscule and

legible, appropriate for liturgical manuscripts. Each

passage starts with an initial letter, usually a T with

ornamental motifs and an illustration relative to the

content.

Miniatures have been painted to the right and left of the

text, in the margins, as well as between the two columns

and rarely, in the upper margin (Figure 2).

An inscription with the name of Antonio Malakes, who

lived in the 13 century, dates the manuscript in the second

half of the same century.

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

EXPERIMENTAL

The equipment used was a modified digital camera Sony

DSC-W300 with capacity to record photographs in the

infrared spectrum at a wavelength 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.

RESULTS AND DISCUSSION

The investigation employed a simple in-situ false colour

photography. The same analytical technique were applied

to several watercolor from Kremer

A small number of pigments were consistently an

conclusively identified; other pigments were identified less

conclusively. The finding confirmed that a small range of

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 hue madder lake and cinnabar were used while for

the blue hue ultramarine and indigo.

Fig. 3. Identification of blue pigments used for the dresses and borders in miniature.

Fig. 4. Identification of red pigments used for the dress, draperies and sandals of Christ.

This is compatible with results of other studies [2]. The

artist choice of pigments was consistent with the pigment

range as the most artists of his era.

One can conclude that the false-color technique provide

an good insight into the artists studio without damaging

the artwork.

[1] T. Moon et al., Studies in Conservation, 37 (1992) 42-52.

[2] L. Bugio et al. PNAS, 107 (2010) 5726.