The Landscape and Objects Laboratory’s portable x-ray fluorescence (pXRF) system has once again visited the Herbert F. Johnson Museum of Art. Dr. Louisa Smieska, a postdoctoral researcher at the Cornell High Energy Synchrotron Source (CHESS) whose studies focus on materials analysis of cultural heritage objects, was recently trained in pXRF data collection at the LoL. On January 15, 2016, Dr. Smieska collaborated with Dr. Andrew Weislogel, the Askin curator of Earlier European and American Art at the Johnson Museum, to collect XRF data from selected regions in several 17th-century Dutch paintings and one 20th-century.
The goal of the study was to survey the pigments used to create these very different paintings, with a particular interest in the blue pigments. Several possible blue choices were available to 17th-century painters, including plant-derived indigo, copper-rich azurite, ground cobalt-rich glass (smalt), and the precious aluminosilicate mineral lapis lazuli (natural ultramarine). Knowing which one was used is important for understanding the original expense of the painting, since ultramarine was much more costly than the other options. Identifying pigments can also hint at how the original composition might have looked, since the color of indigo and smalt can fade over time.
Pictured are Dr. Smieska and Dr. Weislogel collecting pXRF data from a c. 1670 painting by the Dutch artist Otto Marseus van Schrieck. The blue thistle blossoms in this picture are painted with a copper-containing pigment, possibly azurite. The pXRF analysis of other locations in this painting indicated that the green pigment used in the thistle leaves is also copper-based, while the bright red details in a few of the butterfly wings are painted with a mercury-containing pigment, most likely vermilion. The results from this afternoon of analysis will be used to identify paintings that could be good candidates for scanning x-ray fluorescence imaging at CHESS in the next few months.