In addition, the study explored the use of Desorption Electrospray Ionisation Mass Spectrometry Imaging (DESI-MSI) – a novel technique never used before in the analysis of paintworks. This technique was able to detect molecules in trace amounts, which is essential in the analysis of minute samples. In contrast to other techniques, it operates at atmospheric pressure, meaning that it can be used on solid samples with little to no sample preparation. This, in turn, is of great value when analysing delicate subjects such as artwork.
With the Donatello relief, DESI-MSI showed great analytical value by displaying the characterisation of varnishes and other binding components made from natural products such as milk, fish bones or egg yolk. It also detected biomarkers that provide evidence of the presence of drying oils, such as linseed, walnut or poppyseed oil, as well as natural waxes such as beeswax. These materials, which were commonly used in the 15th century, would have been used as binding agents to bond the paint pigment, allowing them to remain on the coated surface when dry.