Leonardo lays it on thin

This is originally an ESRF story, but brought to my attention by Quality Digest.

Leonardo da Vinci's use of translucent glazes in numerous subtle layers to achieve depth and gradation is legendary, a well known delight most obvious in his rendition of facial skin tones. Not all art lovers are interested in the science of this but, for those (like me) who are, the approximate thickness of these layers has always been cause for wonder: easily calculated and emotionally hard to credit. This study, though, goes beyond approximations to measure (noninvasively, using X-ray fluorescence) those thicknesses to close limits.

The answer: Leonardo was consistently working with paint films between 1μm and 2μm – that's one or two thousandths of a millimetre.

[More detail here.]

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• European Synchrotron Radiation Facility (ESRF), http://www.esrf.eu/
• "X-Ray Spectroscopy Gives New Light on Leonardo da Vinci’s Faces", in Quality Digest, 2010-07-20.
• L Viguerie. et al, Revealing the sfumato technique of Leonardo da Vinci by X-ray Fluorescence Spectroscopy. Angewandte Chemie International Edition, 2010, 49, DOI: 10.1002/anie.201001116.