Colorants

Heritage materials science techniques, including pXRF, FTIR-ATR, XRD, microphotography, and microsampling, have peeled back concealed layers of polychromy on a Roman Mithraic altar near Hadrian’s Wall. The results break new ground by exposing the interplay between light and dark and the transformative impact of colour cast onto cultic carved stone. A powerful pigment palette is revealed, including vibrant cinnabar/vermilion letters overlying an unprecedented purple inscription panel created from a compound of Egyptian blue, ultramarine, cinnabar/vermilion, red ochre, red lead, and realgar framed with purple, Egyptian blue, ultramarine, and orpiment. The panel was covered in a golden surface crafted from a previously unknown recipe of pyrite (fool’s gold) mixed with beeswax. Tantalising traces are also detected on some iconographic features, but conservator intervention and degradation processes combined to leach colour from the sculpted relief. These are paradigm-shifting results. They force a reinterpretation of the symbolism and performance of altars as personifications of dedicators, and we identify, for the first time, high-ranking Mithraic initiates by name and grade. Critically, we present a digital reconstruction of the altar with original polychromy that revolutionises our understanding of relief-sculpted Roman inscriptions—a category that has, until now, remained underexplored by the burgeoning polychromy research community.

The trend toward developing sustainable nanotechnology has driven researchers to explore environmentally friendly techniques for nanomaterial fabrication. This review examines the utilisation of Commelina benghalensis plant extracts as an effective biological tool for the green synthesis of various nanomaterials. The procedures involve reducing metal salt precursors with aqueous or polar solvent extracts rich in phytochemicals such as flavonoids and polyphenols, followed by a calcination step that yields crystalline products. The findings show that the properties of ZnO, TiO₂, Ag, NiO, and their composites are directly influenced by synthesis factors, including solvent, plant component, and extract concentration. This directly influenced their specific sizes, morphologies, and phases. Furthermore, these C. benghalensis-mediated nanomaterials showed high efficiency in the photocatalytic degradation of textile dyes and pharmaceuticals, as well as potential antibacterial and antioxidant properties. The Commelina benghalensis plant is flexible and renewable for efficient nanomaterial synthesis; nevertheless, issues with standardisation and scalability must be overcome to fully realise its promise for commercial and industrial uses.

Hair dyes are widely used across all socioeconomic groups and regions worldwide. However, some studies indicate that these products contain substances known to be toxic to a wide variety of organisms. Moreover, dyeing practices generate effluents that may carry the toxicity of hair dyes into the environment. Due to these facts, there is great concern about the impacts these products may have on the environment, as well as on the health of their users and professionals in the field of cosmetology. This scoping review analyzed 184 publications from major databases (PubMed, SciELO, Scopus, Google Scholar, and MEDLINE). Ultimately, 126 scientific studies published between 1981 and 2024 were included based on methodological rigor and their relevance to the One Health framework. According to the literature, the components of hair dyes can induce adverse responses in biological systems, ranging from reversible topical irritations to severe systemic effects. Among the studies evaluated, more than half reported significant toxicological or genotoxic associations related to oxidative dye components such as p-phenylenediamine and its derivatives. These compounds are frequently associated with various types of human cancers, including breast, prostate, bladder, skin, ocular cancers, and brain tumors. In addition to their effects on humans, hair dyes exhibit ecotoxicity, which may threaten the maintenance of ecosystems exposed to their residues. The reported environmental impacts result from effluent emissions after successive hair washes that release unreacted dye residues. Due to the low biodegradability of these compounds, conventional wastewater treatment methods are often ineffective, leading to environmental accumulation and changes in aquatic ecosystems, soil fertility, and trophic balance. Data on the toxicity of hair dye effluents remain scarce and sometimes contradictory, particularly regarding the effects of their transformation products and metabolites. Overall, the evidence underscores the need for continuous monitoring, updated risk assessments, and the adoption of advanced treatment technologies specific to beauty salon effluents. The information presented in this work may support further studies and guide public management agencies in developing policies for mitigating the impacts of hair dye pollutants within the One Health perspective.