Lately 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.