Complementary use of X-ray based imaging and analytical methods in the investigation of miniature portraits

Miniature portraits are still little studied objects. One reason is that thin layers of detailed and very compact paintings do not allow any sampling. Another limitation is that non-invasive techniques must have sufficient spatial resolution and should be as gentle as possible as any surface change can be very noticeable. Usually, the surface of portrait miniatures is not coated with varnish, which is advantageous for the analysis, but at the same time there is a less protection and a higher risk of damage. In this work, three miniature portraits representing the three most important European schools – English, French and Austrian – have been investigated. They are all dated to the beginning of the 19th century, all painted in watercolour on ivory, which is the most common type of the support after 1700. Three innovative analytical approaches have been tested: large area X-ray fluorescence mapping (MA-XRF), X-ray micro-diffraction (micro-XRD) and environmental scanning electron microscopy coupled with energy dispersive X-ray microanalysis (ESEM-EDS). EDS analysis of miniatures in ESEM was tested as an entirely new analytical procedure with using water vapour instead of nitrogen in the specimen chamber. When effectively combining the above-mentioned methods, partial overpaintings and retouchings or a later added signature have been described and localized. A very early use of zinc white (around 1800), a possible origin of Ni-depleted cobalt blue, and numerous manifestations of degradation of As pigments that led to the formation of secondary arsenates have been demonstrated.

Hradilová, J., Hradil, D., Pech, M., Bezdička, P., Neděla, V., Tihlaříková, E., & Targowski, P. (2020). Complementary use of X-ray based imaging and analytical methods in the investigation of miniature portraits. Microchemical Journal, 153, 104371.