Glauconite and Chromatic Recipes in Roman Wall Painting from Astigi (Écija, Spain)

The present study examines the composition and technological strategies used to produce green hues in Roman wall paintings from Augusta Firma–Astigi (Écija, Spain) through Raman spectroscopy. The results identify glauconite as the main green earth pigment and reveal at least two groups with distinct Raman responses, suggesting differences in structural order and geological provenance. The analyses also demonstrate the deliberate combination of green earth with Egyptian blue and, in some cases, goethite, as well as the production of green hues through mixtures of Egyptian blue and yellow pigments. These results reveal a flexible and technically sophisticated approach to colour production, in which natural and synthetic pigments were deliberately combined to modulate hue and saturation. The recurrent detection of amorphous carbon and calcite provides additional information on the mineralogical and technological characteristics of the pigments and painting materials. The identification of different and repeatedly applied pigment combinations constitutes the main contribution of this study, providing new evidence for the technological diversity of green pigments in Roman wall painting. The coexistence of these well-defined recipes in elite contexts of Astigi between the middle of the 2nd century and early 3rd century CE may reflect established workshop practices and a specific preference for green-painted spaces.