Completed removal of overpaint and varnish from the bottom half of the painting. The central portion of the canvas appeared to be in excellent condition save for a few old tears while most of the damage appeared to be localized along the outermost edges of the painting. This may have been caused to prolonged exposure to moisture or even how the painting may have originally been displayed (e.g. in a large hall flanked by windows) (Pictured here: Maggie Bearden).
While microscopic examination is commonly performed on <a href="http://www.artcons.udel.edu/about/kress/examination-techniques-and-scientific-terms/cross-sectional-microscopy" target="_blank">paint cross-sections</a> and dispersed pigment samples, the use of a scanning electron microscope that is capable of energy dispersive X-ray analysis (referred to as SEM-EDX) can be of equal importance. A paint cross-section is placed inside a vacuum chamber and an electron beam is focused on the exposed surface of the sample. Two types of images can be generated using SEM-EDX. An SEM back-scattered electron image (BSE image) provides visual information relating to pigment morphology as well as the range of atomic weights present (e.g. light areas correspond to elements with higher atomic weights such as lead while darker areas indicate lower atomic weight elements). The second type of image, referred to as an EDX map, is generated using very similar technology described in the X-Ray Fluorescence section (link to XRF site) X-rays excite electrons present on the surface of the paint sample, generating elemental information that can help scientists and conservators identify pigments (typically inorganic such as those obtained from crushed up stones and minerals) present in discrete paint/ground layers.<br/><br/>Samples collected from the "Triumph of David" were prepared by project leader Kristin deGhetaldi and examined with scientist Catherine Matsen at the Winterthur Museum Scientific Research and Analytical Laboratory. A Zeiss EVO MA15 scanning electron microscope was used with a LaB6 source at an accelerating voltage of 20kV for the electron beam, stage height of approximately 11mm, and sample tilt of 0 degrees. The EDS data was collected with the Bruker Nano X-flash(R) detector 6|30 and analyzed with Quantax 200/Esprit 1.9 software.
This sample was collected from the shot-silk robe of the woman holding the tambourine after removal of the degraded surface coating. The red-brown ground contains iron oxides, calcium, and alumino-silicates (Fe, Ca, Al, Si, O, Mg, Mn) while the paint layers appear to contain iron oxides (particularly green earth; Fe, Si, Mn, O) and lead white (Pb).<br/<br/><i>Top Left: Visible light/200x magnification; Top Right: BSE image/259x magnification; Bottom left and right: EDS elemental maps (Major Elements: Si, O, Ca, Al, Pb, Fe, K; Trace: Mg, Mn, Na, Ti)<i>
This sample was collected from the blue robe worn by the kneeling woman in the lower right corner before removal of the degraded surface coating. The red-brown ground contains iron oxides, calcium, and alumino-silicates (Fe, Ca, Al, Si, O, Mg, Mn) while the dark blue paint layer appears to contain an extremely pure grade of lapis lazuli (Al, Na, Si, O) followed by a thin layer of lapis mixed with lead white (Pb). In this particular sample the upper layer of the double ground is extremely thin and can only be detected in the EDS map for iron. A large red, iron oxide particle can also be seen in the lower left.<br/><br/><i>Top Left: Visible light/200x magnification; Top Right: BSE image/264x magnification; Bottom left and right: EDS elemental maps (Major Elements: Si, O, Ca, Al, Pb, Fe, K, Mg; Trace: Na)</i>