Identification and mapping of ancient pigments in a Roman Egyptian funerary portrait by application of reflectance and luminescence imaging spectroscopy

Imaging spectroscopy (IS) is an important tool in the comprehensive technical analysis required of archaeological paintings. The complexity of pigment mixtures, diverse artistic practices and painting technologies, and the often-fragile and weathered nature of these objects render macroscale, non-invasive chemical mapping an essential component of the analytical protocol. Furthermore, the use of pigments such as Egyptian blue and madder lake, featuring diagnostic photoluminescence emission, provides motivation to perform photoluminescence mapping on the macroscale. This work demonstrates and advances new applications of dual-mode imaging spectroscopy and data analysis approaches for ancient painting. Both reflectance (RIS) and luminescence (LIS) modes were utilized for the study of a Roman Egyptian funerary portrait from second century CE Egypt. The first derivative of the RIS image cube was analyzed and found to significantly improve materials separation, identification, and the extent of mapping. Egyptian blue and madder lake were mapped across a decorated surface using their luminescence spectral signatures in the region of 540–1000 nm as endmembers in LIS analyses. Linear unmixing of the LIS endmembers and subsequent derivative analyses resulted in an improved separation and mapping of the luminescence pigments. RIS and LIS studies, combined with complementary, single-spot collection elemental and molecular spectroscopy, were able to successfully characterize the portrait’s painting materials and binding media used by the ancient artist, providing key insight into their material use, stylistic practices, and technological choices.

Compressive nano-FTIR chemical mapping

Nano-Fourier-transform infrared spectroscopy (nano-FTIR) combines infrared spectroscopy with scanning probe microscopy (SPM) techniques and enables spectroscopic imaging of molecular and electronic properties of matter at nanometer spatial resolution. The spectroscopic imaging can be used to derive chemical mappings, i.e., the spatial distribution of concentrations of the species contained in a given sample. However, due to the sequential scanning principle underlying SPM, recording the complete spectrum over a large spatial area leads to long measurement times. Furthermore, the acquired spectrum often contains additional signals from species and lineshape effects that are not explicitly accounted for. A compressive chemical mapping approach is proposed for undersampled nano-FTIR data that utilizes sparsity of these additional signals in the spectral domain. The approach combines a projection technique with standard compressed sensing, followed by a spatially regularized regression. Using real nano-FTIR measurements superimposed by simulated interferograms representing the chemical mapping of the contained species, it is demonstrated that the proposed procedure performs well even in cases in which the simulated interferograms and the sparse additional signals exhibit a strong spectral overlap.

Intermittent Beginning to the Formation of Hydrogenous Ferromanganese Nodules in the Vast Field: Insights from Multi-Element Chemostratigraphy Using Microfocus X-ray Fluorescence

Vast ferromanganese nodule fields have been found on the deep-sea floor of all oceans worldwide. They have received attention because they potentially provide high-grade metal resources to develop future high- and green-technology. However, how these vast nodule fields were formed and developed owing to their widespread nature or tendency to be denser with an increasing number of nodules has not yet been established. In this study, the fine-scale inner structure of nodules of various sizes was analyzed on the basis of chemical mapping using microfocus X-ray fluorescence. We found that nodules distributed in the vast field around Minamitorishima (Marcus) Island have several types of innermost layers, which correspond to different chemostratigraphic layers of nodules that have been previously reported by us in this region. As nodules grow in order from the center to the outside, the different types in the innermost layer indicate a difference in the timing of the beginning of their growth. Moreover, because the differences in the chemical features of each layer reflect differences in the composition of the original deep-sea water, our results imply that the beginning of nodule formation occurred intermittently at each time of a water mass replacement due to new deep-sea currents flowing into this region. We recognized that the northern part of the study area was dominated by large nodules that started to grow in relatively earlier times, while the southern part tended to have many nodules that grew in relatively later times. Based on these observations, we hypothesize that the intermittent beginning of nodule formation is governed by the northward inflow of the deep-sea current that originated from the Lower Circumpolar Deep Water for an extended time to form the vast nodule field. Because patterns in the timing of nodule formation were different in the eastern and western regions, we thus further propose that the topographic framework, i.e., the arrangement of individual large seamounts and the cluster of small knolls and petit-spot volcanoes, strongly regulates the flow path of the deep-sea current, even if the position of the entire seamount changes owing to plate motion. The deep-sea current might supply some materials to be nuclei, resulting in the nodule formation at the beginning of the process.

Utilizing local phase transformation strengthening for nickel-base superalloys

Almost 75 years of research has been devoted to producing superalloys capable of higher operating temperatures in jet turbine engines, and there is an ongoing need to increase operating temperature further. Here, a new disk Nickel-base superalloy is designed to take advantage of strengthening atomic-scale dynamic complexions. This local phase transformation strengthening provides the alloy with a three times improvement in creep strength over similar disk superalloys and comparable strength to a single crystal blade alloy at 760 °C. Ultra-high-resolution chemical mapping reveals that the improvement in creep strength is a result of atomic-scale η (D024) and χ (D019) formation along superlattice stacking faults. To understand these results, the energy differences between the L12 and competing D024 and D019 stacking fault structures and their dependence on composition are computed by density functional theory. This study can help guide researchers to further optimize local phase transformation strengthening mechanisms for alloy development.

Analysis of Cr(VI) Bioremediation by Citrobacter freundii Using Synchrotron Soft X-ray Scanning Transmission X-ray Microscopy

Scanning transmission X-ray microscopy (STXM) was utilized for analysing the bioremediation of Cr(VI) by Citrobacter freundii, a species of gram-negative bacteria. The biosorption and bioreduction processes were analysed by the chemical mapping of cells biosorbed at different concentrations of Cr(VI). STXM spectromicroscopy images were recorded at O K-edge and Cr L-edge. A thorough analysis of the X-ray absorption features corresponding to different oxidation states of Cr in the biosorbed cell indicated the coexistence of Cr(III) and Cr(VI) at higher concentrations. This signifies the presence of partially reduced Cr(VI) in addition to biosorbed Cr(VI). In addition, the Cr(III) signal is intense compared with Cr(VI) at different regions of the cell indicating excess of reduced Cr. Speciation of adsorbed Cr was analysed for the spectral features of biosorbed cell and comparison with Cr standards. Analysis of absorption onset, L3/L2 ratio and absorption fine structure concludes that adsorbed Cr is predominantly present as Cr(III) hydroxide or oxyhydroxide. The evolution of absorption features in the duration of biosorption process was also studied. These time lapse studies depict the gradual decrement in Cr(VI) signal as biosorption proceeds. A strong evidence of interaction of Cr with the cell material was also observed. The obtained results provide insights into the biosorption process and chemical speciation of Cr on the cells.

Alteration mineralogy and pathfinder element inventory in the footprint of the McArthur River unconformity-related uranium deposit, Canada

ABSTRACT Pathfinder elements associated with the exploration footprint of the McArthur River unconformity-related U deposit include U, radiogenic Pb, V, Ni, Co, Cu, Mo, As, Zn, and rare earth elements. In this study, the mineralogical and paragenetic context for their occurrence was established by integrating in situ mineral chemistry and laser ablation mass spectrometry chemical mapping of interstitial assemblages, detrital grains, and cements with whole-rock analyses of drill core samples from the diagenetically altered background and the hydrothermally altered sandstone host rocks. Diagenetically altered background sandstones contain a matrix assemblage of illite and dickite, with trace to minor aluminum-phosphate-sulfate (APS) minerals, apatite, and Fe-Ti oxide minerals. Aluminum-phosphate-sulfate minerals account for the majority of the Sr and light rare earth element concentrations, whereas early diagenetic apatite, monazite, and apatite inclusions in detrital quartz and detrital zircon contribute significant U and heavy rare earth elements to samples analyzed with an aggressive leach (partial digestion) such as aqua regia. Hydrothermally altered sandstone host rocks also contain variable assemblages of Al-Mg chlorite (sudoite), alkali-deficient tourmaline, APS minerals, kaolinite, illite, Fe-oxide, and sulfide minerals. Late pre-mineralization chlorite accounts for a significant portion of the observed Ni concentrations, whereas Co, Cu, Mo, and Zn occur predominantly in cryptic sub-micron sulfide and sulfarsenide inclusions within clay mineral aggregates and in association with Fe-Ti oxides. Elevated concentrations of U were observed in cryptic micro-inclusions associated with sulfides in quartz overgrowths, with Fe-Ti oxide micro-inclusions in kaolinite, and in post-mineralization Fe-oxide veins. The distribution of pathfinder elements throughout the deposit footprint appears to be less related to the primary dispersion of alteration minerals from the hydrothermal system than to the secondary dispersion of elements post-mineralization. Their occurrence throughout pre-, syn-, and post-mineralization assemblages further demonstrates the limitations to defining geochemical footprints from pathfinder element concentrations expressed in lithogeochemical data sets without structural, lithological, and mineralogical context.