Influence of Mineralogical Composition and Porosity on the Preservation of Selected Fatty Acids in Experimental and Archaeological Ceramics

Jan-Michael C. Cayme1,2*, Rasmus Palm1, Peeter Somelar1, Anu Teearu1, Signe Vahur1, Ivo Leito1, and Ester Oras1

The factors influencing the preservation of organic residues in archaeological ceramics were investigated, focusing on the fatty acids C16:0 and C18:1. To examine how pottery composition affects lipid absorption and retention, forty-four experimental clay briquettes were produced using different clay types, tempers (sand and chalk), and firing temperatures of 600°C and 800°C. These briquettes were designed to simulate variations commonly observed in archaeological pottery from Estonia. Results show that both the porosity of the ceramic matrix and its mineralogical composition play significant roles in organic residue preservation. The formation of micro- and mesopores within the pottery matrix was influenced by the clay type, temper, and mineral transformations during firing. Briquettes containing chalk temper, particularly when fired at higher temperatures, exhibited greater pore development and improved fatty acid retention. This is attributed to the formation of calcium fatty acid salts, which enhance lipid binding to the ceramic matrix. In contrast, sand temper had minimal influence on pore formation and lipid preservation. The experimental results were compared with archaeological pottery from a 12th–13th century burial site in Kukruse, Estonia. These samples showed mineral compositions and pore structures comparable to the experimental briquettes, supporting the findings that mineralogy and pore structure strongly influence the preservation and recovery of organic residues in archaeological pottery.