Karen Trentelman

Revealing hidden paint layers in oil paintings by means of scanning macro-XRF: a mock-up study based on Rembrandt's “An old man in military costume”

Over the past several decades the oeuvre of Rembrandt has been the subject of extensive art historical and scientific investigations. One of the most striking features to emerge is his frequent re-use of canvases and panels. The painting An Old Man in Military Costume (78.PB.246), in the collection of the J. Paul Getty Museum, is an example of such a re-used panel. Conventional imaging techniques revealed the presence of a second portrait under the surface portrait, but the details of this hidden portrait have not yet been revealed. Vermilion (HgS) has been identified to have been used nearly exclusively in the flesh tones of the lower painting, suggesting that element-specific XRF imaging might successfully image the hidden portrait. To test this hypothesis, a full-scale mock-up of the painting was created, including a “free impression” of the hidden portrait, reproducing as closely as possible the pigments and paint stratigraphy of the original painting. XRF imaging of the mock-up painting was conducted using three different XRF imaging systems: a mobile X-ray tube based system and two synchrotron-based setups (one equipped with multiple SDDs and one equipped with a Maia detector). The sensitivity, limits of detection and imaging capabilities of each system under the chosen experimental conditions are evaluated and compared. The results indicate that an investigation of the original painting by this method would have an excellent chance of success.

Evidence for an unorthodox firing sequence employed by the Berlin Painter: deciphering ancient ceramic firing conditions through high-resolution material characterization and replication

XANES spectroscopy was used to complement the results previously obtained with Raman spectroscopy by the same group to determine the firing conditions used in the production of a single vessel painted by the Berlin Painter in the 5th century B.C. The vessel, part of the collection of the J. Paul Getty Museum, presents a complicated layered architecture of black and red gloss, with different stratigraphies present on the interior and exterior surfaces. The study of two samples, one each from the interior and exterior surface of the vessel, was performed with the complementary analytical techniques of X-ray nano- and micro-spectroscopy (X-ray fluorescence spectroscopy (XRF) and full-field transmission X-ray micro-spectroscopy (FF-XANES) across the Fe K edge), and supported by a replication study. The replicates, made in a laboratory furnace providing complete control over the firing temperature and oxygen partial pressure, provided a paradigm for the comparison of the mineralogical phases observed in the ancient samples, which led to a deeper understanding of the firing conditions necessary for the production of the Berlin Painters vessel. Our results confirm the necessity of multiple firings and painting applications to obtain the Berlin Painters architecture and provide a further example of the multiplicity of techniques and practices employed by the potters of the Kerameikos in ancient Athens.

Multiple layers in black gloss as evidence of multiple firings

The iconic red and black figure vessels, produced in Athens from the 6th through the 4th centuries B.C., represent the pinnacle of ancient ceramic craftsmanship. The ancient Greeks painted the ceramics with refined Fe-rich clay that, when fired, created deep black decorative glossy surfaces. The refinement process likely involved isolation of very fine grain clays through levigation; dispersing the clay into large vats of water, allowing the coarse grains to settle to the bottom, leaving fine grains suspended in solution for subsequent collection. The established model [1] describes the firing process as a single firing in which the kiln environment was subjected to a three stage cycle of oxidation–reduction–oxidation. When fired at high temperature under reducing conditions the slips sintered and turned from red (hematite, Fe2O3) to black (magnetite, Fe3O4, hercynite FeAl2O4). During the last step, oxygen was unable to diffuse into the more vitrified slips, keeping them black, whereas the iron minerals in the porous body ceramic were reoxidized to Fe2O3, producing a contrasting red color. As previously reported [2] the production of this pottery was likely more complex than formerly thought, with vessels subjected to two, or possibly more, firings in the kiln, with applications of slip between each firing.

Investigating the firing protocol of athenian pottery production: A raman and hi-resolution TEM study

The decorated ceramics produced in ancient Athens from the 6th through the 4th centuries BCE, also known as Attic pottery, are considered a benchmark technological achievement of the pre-industrial world. The iconic black-figure vessels (black figures painted on red reserve), and the later, more refined, red-figure vessels (figures left in reserve on a black background), demonstrate a sophisticated control of particle morphology, porosity and firing conditions. Both techniques achieved the production of smooth and glossy black surfaces layers – called black gloss – by alternating the high-temperature kiln between oxidative and reductive environments during firing. Areas painted with a refined slip turned from red (due to the presence of Fe3+ compounds: hematite, -Fe2O3 and maghemite, γ-Fe2O3) to black (Fe2+ iron compounds: magnetite, Fe3O4, hercynite, FeAl2O4) depending on the atmospheric condition of each stage. Although a basic understanding of their production has been developed, details regarding the painting and firing schemes employed are still not completely understood [1] .

A Technical Study of the Rosebud Winter Count

Abstract Plains Indian drawings and historical records produced in the nineteenth and early twentieth centuries made progressively greater use of nontraditional drawing materials such as commercial colored pencils, crayons, ink and watercolors. Similarly, cloth and paper begin to supplant traditional hide supports during this period. These non-traditional materials rarely have been studied in this context, yet their dates of manufacture and subsequent availability through traders and missionaries, or distribution by the Bureau of Indian Affairs, has the potential to inform about the creation date of a drawing or historical record. An analysis of the materials and methods used to produce the Rosebud winter count, a Lakota pictographic calendar, is described. Results indicate that the 136 motifs on the Rosebud winter count were produced, likely in sequence, by two different hands, followed by general outlining and finally, motif numbering. The materials used in the winter count were for the most part unavailable before the nineteenth century. Colored pencil containing the pigment Prussian blue was found to form an integral part of the winter count, thus allowing the date of manufacture to be placed most likely after 1883.