15. Nondestructive Studies of Ancient Pigments on Romano-Egyptian Funerary Portraits of the Kunsthistorisches Museum, Vienna

Introduction

In 2014 the conservation department of the Kunsthistorisches Museum, Vienna (KHM), joined the APPEAR project by adding ten mummy portraits to the collaborative study. Preliminary scientific investigations of these works began at the KHM in 1999.1 Conservation treatment was completed on all ten portraits as well as on five examples from the collection of antiquities of the Museum of Fine Arts, Budapest, to learn more about the acquisition history of the Budapest funerary portraits.2

Conservation scientist Dr. Roberta Iannaccone implemented noninvasive for preliminary identification. Dr. Caroline Cartwright, a wood anatomist, identified the tree species used for all fifteen ; for the KHM examples, the results confirmed that six were sycomore fig, three were linden, and one was tamarisk.

Methods

MSI is a set of techniques based on photography at various wavelengths; every range of wavelengths (from ultraviolet to near infrared) can reveal different characteristics.3 , , , visible (VIS), , , and imaging were used to characterize pigments and shed light on modern retouches.

To acquire the images two cameras were used: a Nikon D80 with a resolution of 10 megapixels and a 23.5-by-15.7-millimeter sensor dimension, and a modified Nikon D3200 with a resolution of 24.2 megapixels with removed IR filter and a 23.5-by-15.7-millimeter sensor dimension. Both cameras were equipped with a Nikkor AF 28–105-millimeter, f/3.5–4.5D lens as well as specific filters for every technique.4

Noninvasive was performed using the KHM’s PART II instrument.5 The spectrometer, equipped with a vacuum chamber to reduce the absorption of low energetic radiation in air, possesses a low-power X-ray tube with molybdenum (Mo) target (excitation parameters used: 40 kV, 0.4 mA, 100s). The primary beam is focused via a polycapillary lens (spot size ~150 µm). The measuring point is placed 1 millimeter outside of the chamber, thus minimizing absorption losses in the excitation and µ-XRF radiation paths.

Results

For all fifteen investigated portraits the common use of was confirmed. Additionally, , or , copper green, , , and gold were detected. Also identified were three different types of layers: , , and lead white.

For the purpose of this publication, the studies of two portraits—visually classified as and based—are described below.

The Portrait of a Lady (fig. 15.1) is encaustic based. The characteristic pink luminescence attributed to a red pigment is visible on the but not on the lips; there µ-XRF confirms the presence of iron, suggesting the use of . The NIR image does not show an underdrawing; however, on the lips the outlining pigment seems mixed with a substance that strongly absorbs infrared radiation, suggesting the presence of charcoal in the admixture.

Figure 15.1 Portrait of a Lady, Romano-Egyptian, AD 117–138. er-Rubayat. Encaustic on wood, 40 x 20 cm (15 ¾ x 7 7/8 in.). Vienna, Kunsthistorisches Museum, Antikensammlung, X 297. KHM-Museumsverband

The violet tunic seems to partially absorb infrared radiation, with IRRFC showing a green/grayish response. Aluminum, typically associated with the lake substrate, together with a strong pink luminescence suggests the presence of red lake. Usually, when a red lake paint layer is superimposed on or mixed with red ochre or , it appears yellow/orange in IRRFC. The VIL image shows the typical luminescence of Egyptian blue in areas of the tunic. µ-XRF measurements confirm this observation, revealing some copper. Most likely, the red lake was combined with Egyptian blue, lead white, and red ochre (detected by µ-XRF) to obtain the purple tint. Egyptian blue was mainly used to render the face and create shadows (fig.15.1c).

Identification of the dark blue on the left side of the tunic was inconclusive. XRF analysis did not identify any characteristic elements, and UVRFC and IRRFC imaging techniques did not indicate the presence of . Furthermore, a pale blue fluorescence can be observed on top of the painted surface, in areas not covered by the mummy wrappings.6 Classification and origin of this material will be a matter of further investigation.

The Portrait of a Young Man with Wreath (fig. 15.2) is tempera based. The UVL image shows some areas with bright pink fluorescence (likely due to a red lake) mainly on the , cheeks, and lips; a bright yellow luminescence can be observed on the bridge of the nose, the lip outlines, and the eye. µ-XRF analysis in the area of yellow luminescence identified the presence of lead (lead white) and iron (earth pigments). Lead white typically fluoresces light blue; therefore, this particular yellow fluorescence could be related to the binder or a pigment mixture.7

Figure 15.2 Portrait of a Young Man with Wreath, Romano-Egyptian, AD 125–150. er-Rubayat. Tempera on wood, 32.5 x 18 cm (12 13/16 x 7 1/16 in.). Vienna, Kunsthistorisches Museum, Antikensammlung, X 432. KHM-Museumsverband

The µ-XRF spectrum of the irises indicates the presence of iron (earth pigment). The unexpected red color visible in the IRRFC image of the dark hair, the original portion of the clavi, the irises, and the light blue background is attributable to the spectral response of a blue pigment, probably an organic blue (indigo) partly mixed with an earth pigment.8

Our understanding of the materials and painting process of the mummy portraits described above has been much enhanced by the scientific identification of the woods and by the use of two nondestructive methods (µ-XRF and MSI) for identifying the pigments.

Notes


  1. .
  2. See Endreffy and Nagy, this volume.
  3. For similar methods applied on Attic ceramics, see .
  4. ; .
  5. ; .
  6. For further information about the material, see .
  7. See ; , 67–81.
  8. Indigo has been identified in the pupil, hair, clavi, and beads of a comparable portrait in the Getty collection: Mummy Portrait of a Woman (79.AP.129). The paintings are similar in both their execution and their response to MSI.