The
pyroantimonate pigments Naples yellow and lead tin antimonate
yellow are recognized as some of the most stable synthetic yellow
pigments in the history of art. However, this exceptional lightfastness
is in contrast with experimental evidence suggesting that this class
of mixed oxides is of semiconducting nature. In this study the electronic
structure and light-induced behavior of the lead pyroantimonate pigments
were determined by means of a combined multifaceted analytical and
computational approach (photoelectrochemical measurements, UV–vis
diffuse reflectance spectroscopy, STEM-EDS, STEM-HAADF, and density
functional theory calculations). The results demonstrate both the
semiconducting nature and the lightfastness of these pigments. Poor
optical absorption and minority carrier mobility are the main properties
responsible for the observed stability. In addition, novel fundamental
insights into the role played by Na atoms in the stabilization of
the otherwise intrinsically unstable Pb2Sb2O7 pyrochlore were obtained.
Petroglyph sites exist all over the world. They are one of the earliest forms of mankind’s expression and a precursor to art. Despite their outstanding value, comprehensive research on conservation and preservation of rock art is minimal, especially as related to biodeterioration. For this reason, the main objective of this study was to explore the factors involved in the degradation of petroglyph sites in the Negev desert of Israel, with a focus on biodegradation processes. Through the use of culture-independent microbiological methods (metagenomics), we characterized the microbiomes of the samples, finding they were dominated by bacterial communities, in particular taxa of Actinobacteria and Cyanobacteria, with resistance to radiation and desiccation. By means of XRF and Raman spectroscopies, we defined the composition of the stone (calcite and quartz) and the dark crust (clay minerals with Mn and Fe oxides), unveiling the presence of carotenoids, indicative of biological colonization. Optical microscopy and SEM–EDX analyses on thin sections highlighted patterns of weathering, possibly connected to the presence of biodeteriorative microorganisms that leach the calcareous matrix from the bedrock and mobilize metal cations from the black varnish for metabolic processes, slowly weathering it.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.