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Paint spotting

24 March 2017 - The arts

Snickt2017.PNGLately this blog has taken an interest in the arts. It was about time, otherwise it is just more science filling these pages. Paintings are an art form and the Ghent Altarpiece is an early one (completed in 1432). Away with all the chemistry, it was decided that this important masterpiece would be a good starting point for expansive artistic exploration. Is it just me or do all the angels depicted in one of the panels look exactly the same? The experts have their expert opinions but it seems the van Eyck brothers simply economized on the number of models sitting for their work.
Just kidding there, was just reading about Van der Snickt et al. and their analysing the crap out the painting with Ma-XRF and SEM-EDX in the Angewandte (DOI). So back to serious chemistry. MA-XRF (Scanning macro-XRF) is a technique so advanced it does not have a Wikipedia page. For background see the University of Antwerp page where all of this has been taking place here. This machine is able to scan an entire painting with an x-ray beam and record the emitted X-ray fluorescence. The penetration level can be varied so the end result is three-dimensional. All the individual paints based on their metal content can now be visualised. For the Ghent Altarpiece the numbers are 8 square meters of painting, 16 million XRF spectra and 1 GB of data. The rationale: the analysis of restorations carried out over the centuries. These restorations were badly needed, Reformation fanatics were not art lovers (think Taliban), the Nazi's arrived and went, not to mention various instances of plunder and theft.

The data reveals previous restoration attempts in red zones with iron-based hematite materials in area's originally colored red with mercury-based vermilion. More alarmingly, several sections turn out to be largely overpainted. One of those overpaints involves copper-based azurite. As this material was replaced by the art world in the beginning of the eighteenth century by Prussian blue the culprit of this defacement must be that old. Interestingly as a result of this analysis it was decided to remove all overpaints from the painting, a work already completed.



More hydrogen spotting

17 March 2017 - Image of the week

hydrogen chen 2017.PNGIn the image of the week we see actual deuterium atoms (in red) embedded in steel. The image was produced by Chen et al. as reported in Science (DOI). The presence of hydrogen in steel in general is a serious matter as it causes brittleness and ultimately nasty things like bridges collapsing Hydrogen embrittlement can be combated by thermal treatment and by adding vanadium carbide nanoparticles. These particles trap hydrogen and slow their diffusion. As for the visualisation the researchers relied on atom probe tomography (APT). In this technique atoms are stripped one by one from the metal surface and analysed by mass spectroscopy. This generates a 3D microscope image. Now, hydrogen is way too abundant and will photo-bomb any image but replacing hydrogen with deuterium solves that. Regular ferritic steel was used and an electrolytic method was applied to charge it with deuterium. With cryo transfer @100K gas diffusion was suppressed. In the image the blue areas indicate vanadium, clearly indicating H and V have a certain fondness for each other.

Previous hydrogen spotting here