Focusing on red and black engobes in Roman pottery from Cumae (southern Italy): Pompeian Red Ware and Graue Platten ceramic productions

•Ceramic slips Pompeian Red Ware and Graue Platten have been characterized.•Results were achieved using a non-destructive approach (Raman, pXRF).•Coatings were also analysed via X-ray diffraction on zero-background holders.•Two different ceramic slip productions were observed for Pompeian Red Ware.•Dark colour of Graue Platten slip is due to presence of carbon black material.