Physicochemical analysis of grey pigments from pre-Columbian archaeological ceramics from the sites of Alto del Cardal and Nuevo Corinto (Costa Rica): First identification of fired bone mixtures in Central America

Ceramic samples from the sites Alto del Cardal and Nuevo Corinto in Costa Rica, dating between 700 and 1500 CE (Common Era), were analysed. These sherds, excavated from domestic, funerary, and workshop contexts, exhibited substantial socio-productive activities, including tool manufacturing. The ceramics were characterized by significant thickness, ranging from 9.25 to 12.46 mm. Analysis using infrared spectroscopy, Raman, and Scanning Electron Microscopy revealed the presence of biogenic hydroxyapatite from fired bones, amorphous carbon, meta-smectite, quartz, anatase, hematite, and traces of magnetite. Finding hydroxyapatite from fired bone as a ceramic pigment or coating is unprecedented in Costa Rica, Central America, and Mexico. This technique suggests a high degree of layer heterogeneity and an application without slip, reminiscent of a singular occurrence documented in southern Argentina and analogous practices in Brazil and Chile. This similarity allowed us to hypothesize a potential use of the studied ceramics in metal production.