Beyond pigment: Integrated organic and inorganic analysis of cosmetic residues in pre-Islamic archaeological shells from Southeast Arabia

This study presents the results of a multi-analytical strategy implemented to investigate the composition of pigments preserved within the shells of marine bivalves recovered from six archaeological sites from the Late Bronze Age to the 6th-7th century CE in the present-day United Arab Emirates. The analysed bivalve specimens contain greenish or blackish materials in the shell interior and according to current archaeological interpretations they have functioned as cosmetic containers in daily life and as grave goods, a hypothesis supported by their recovery in both settlement and burial contexts. Their presence in funerary contexts, however, paired with ethnological observations, suggests these pigments were also endowed with curative powers. The main purpose of this study is to characterize the chemical composition of pigments and to assess their compatibility with proposed uses, particularly their potential application in cosmetics, while recognizing that such interpretations cannot be based on chemical data alone and must also rely on contextual archaeological evidence. To achieve this, a suite of complementary analytical techniques was employed. Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX), Laser-Induced Breakdown Spectroscopy (LIBS), Fourier-Transform Infrared Spectroscopy in Attenuated Total Reflectance (ATR-FTIR), Raman Spectroscopy, X-Ray Diffraction (XRD) techniques were used to explore the elemental and mineralogical features of samples while Gas Chromatography coupled with Mass Spectrometry (GC/MS) provided insights into organic components, not achievable through inorganic-focused techniques. The results reflect the varying analytical confidence achievable for these complex samples: while the inorganic fraction was robustly characterized, the organic findings remained more constrained. A total of 34 samples were examined and grouped into 2 main categories based on pigment colour: green and black. The green pigments commonly exhibited elevated concentrations of copper, frequently associated with minerals such as atacamite, paratacamite, or brochantite. In contrast, the black pigments revealed the presence of carbon-based black pigments and, in minority cases, Mn-bearing minerals, such as braunite, and organic-based pigments, as bitumen. The fatty acids detected in three green pigments and one black pigment suggest the presence of lipid material of animal origin, possible due to mollusc soft tissue remains, while the use of an adding binder cannot be assessed. Overall, the results obtained through this integrated multi-analytical approach, not only improve understanding of the substances stored within malacofaunal containers but also support the hypothesis that at least some of the materials were possibly related to cosmetic practices, allowing for the reconstruction of aspects of daily and ritual life in ancient Magan.