Journal of Mass Spectrometry (2010), 45, 944–950., Jan 1, 2010
"The rock art site at the village of Songo in Mali is a very important Dogon ritual place where, ... more "The rock art site at the village of Songo in Mali is a very important Dogon ritual place where, since the end of the 19’s century until today, takes place the ceremony of circumcision. During these ceremonies, paintings are performed on the walls of the shelter with mainly three colors: red, black and white. Ethnological literature mentions the use of animal urine of different species such as birds, lizards or snakes, as a white pigment. Urine of these animals is mainly composed of uric acid or urate salts. In this article, Time of flight Secondary Ion Mass Spectrometry (ToF-SIMS) is used to compare uric acid, snake urine and a sample of a white pigment of a Dogon painting coming from the rock art site of Songo. ToF-SIMS measurements in both positive and negative ion modes on reference compounds and snake urine prove that ToF-SIMS is well suited to study uric acid and urate salts. This method enables to identify unambiguously these compounds in particular through the detection in negative ion mode of the ion corresponding to the deprotonated molecule ([M-H]- at m/z 167,01) and its fragments. Moreover, the mass spectra obtained in positive ion mode permit to differentiate uric acid and urate salts through the presence of specific ions. Applying this method to the Dogon white pigments sample, we show that the sample is entirely composed of uric acid. This proves for the first time, that animal urine was used as a pigment by the Dogon. The presence of uric acid instead of urate salts as normally expected in animal urine could be explained by the preparation of the pigment for its application on the stone.
Keywords: Mass Spectrometry Imaging, ToF-SIMS, Uric Acid, African Rock Art, Dogon, cultural heritage."
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Papers by Eric Laval
Giotto (1266–1337) and his workshop realized c. 1315 the large Crucifix now in the Louvre Museum. The conservation of this masterpiece in 2010–2013 in the C2RMF studios gave the opportunity for a comprehensive investigation of the execution technique through a characterization of the paint layers. The first examinations revealed an original gilding and decoration surrounding the Christ which was repainted during the 19th C., raising the question of the original decoration appearance.
Results:
The original decoration still present underneath was unve
iled. The different imaging analytical techniques applied brought complementary results allowing us to reconstruct the original decoration. Elemental images of selected areas on the Crucifix were obtained using bi-dimensional X-ray flu
orescence imaging technique (2D-XRF) with a prototype
XRF spectrometer mounted on a motorized X-Y system. The head of the instrument was moved over a 150 x150 mm2
area with 1 mm steps, using a 1 mm beam spot and acquisition time of 2 seconds per pixel. The XRF spectra of each pixel provided semi-quantitative elemental maps of the layers: gilding and pigments even at low concentrations could
be recognised. The XRF maps achieved were completed by X-ray radiographs and emissiographs of the Crucifix. Some
micro-samples analyzed with the scanning electron micr
oscope (SEM-EDX) allowed a better understanding of the
stratigraphy. The comparison of the direct light and the X
-ray pictures enabled us to distinguish the repaint from
the original pattern. The visible metallic leaf is a thin gold leaf applied on a mordant gilding while the original
one is a double leaf of gold and silver (Zwischgold) applied on a red bole. As for the painting, the visible decoration is
composed of brown earth and organic greenish color whereas the original is made of red lake, copper green, azurite and vermillion. The 2D-XRF maps evidenced two levels of copper that could be ascribed to two different copper pigments, a blue and a green one.
Conclusions:
A complementary methodology combining classical X-ray imaging, sample analysis and 2D-XRF was applied to large areas of the Giotto’s crucifix. This approach allowed us to distinguish the underlying original composition from the 19
th C. overpainted decoration.
Keywords: Mass Spectrometry Imaging, ToF-SIMS, Uric Acid, African Rock Art, Dogon, cultural heritage."
Giotto (1266–1337) and his workshop realized c. 1315 the large Crucifix now in the Louvre Museum. The conservation of this masterpiece in 2010–2013 in the C2RMF studios gave the opportunity for a comprehensive investigation of the execution technique through a characterization of the paint layers. The first examinations revealed an original gilding and decoration surrounding the Christ which was repainted during the 19th C., raising the question of the original decoration appearance.
Results:
The original decoration still present underneath was unve
iled. The different imaging analytical techniques applied brought complementary results allowing us to reconstruct the original decoration. Elemental images of selected areas on the Crucifix were obtained using bi-dimensional X-ray flu
orescence imaging technique (2D-XRF) with a prototype
XRF spectrometer mounted on a motorized X-Y system. The head of the instrument was moved over a 150 x150 mm2
area with 1 mm steps, using a 1 mm beam spot and acquisition time of 2 seconds per pixel. The XRF spectra of each pixel provided semi-quantitative elemental maps of the layers: gilding and pigments even at low concentrations could
be recognised. The XRF maps achieved were completed by X-ray radiographs and emissiographs of the Crucifix. Some
micro-samples analyzed with the scanning electron micr
oscope (SEM-EDX) allowed a better understanding of the
stratigraphy. The comparison of the direct light and the X
-ray pictures enabled us to distinguish the repaint from
the original pattern. The visible metallic leaf is a thin gold leaf applied on a mordant gilding while the original
one is a double leaf of gold and silver (Zwischgold) applied on a red bole. As for the painting, the visible decoration is
composed of brown earth and organic greenish color whereas the original is made of red lake, copper green, azurite and vermillion. The 2D-XRF maps evidenced two levels of copper that could be ascribed to two different copper pigments, a blue and a green one.
Conclusions:
A complementary methodology combining classical X-ray imaging, sample analysis and 2D-XRF was applied to large areas of the Giotto’s crucifix. This approach allowed us to distinguish the underlying original composition from the 19
th C. overpainted decoration.
Keywords: Mass Spectrometry Imaging, ToF-SIMS, Uric Acid, African Rock Art, Dogon, cultural heritage."