Eric Laval

Revealing the sfumato Technique of Leonardo da Vinci by X‐Ray Fluorescence Spectroscopy

The perfection of Leonardo da Vincis painting technique hasalwaysbeenfascinating.Thegradationoftonesorcolorsfromlight to dark is barely perceptible. Neither brushstroke norcontourisvisible:lightsandshadesareblendedinthemannerof smoke. Understanding this technique, usually calledsfumato, remains one of the challenges still unaddressed inart history. Herein we show that quantitative X-ray fluores-cence spectroscopy performed directly on the works of artmakes it possible to access the description of the paint layersused in the flesh tones. We determined the composition andthe thickness of the paint layers of nine faces, painted byLeonardo (or attributed to him) over 40 years of his activity.Theresultsshednewlightonhisconstantresearchtoimprovethe visual aspects of his works of art. In his later paintings, hewas able to apply translucent layers (glazes), which weremainly composed of an organic medium in very thin films,down to a micrometer scale.How did Leonardo da Vinci obtain such impressivenaturalistic effects in his paintings? The description of themasters sfumato technique is the subject of active discussionin arthistory.

Animal urine as painting materials in African rock art revealed by cluster ToF-SIMS mass spectrometry imaging.

The rock art site at the village of Songo in Mali is a very important Dogon ritual place where, since the end of the nineteenth 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 proved useful for the study of uric acid and urate salts. This method enables to identify unambiguously these compounds owing to the detection in negative ion mode of the ion corresponding to the deprotonated molecule ([M-H](-) at m/z 167.01) and its fragment ions. Moreover, the mass spectra obtained in positive ion mode permit to differentiate uric acid and urate salts on the basis 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.