Organic residue analysis of experimental, medieval, and post-medieval glazed ceramics

Glazed ceramics have not typically been sampled for organic residue analysis because the glaze is not porous; therefore, it is commonly believed that these ceramics cannot absorb substances. Although this is partially true, the aim of this paper is to demonstrate that the glaze may exhibit imperfections due to the production process or the use of ceramics and that these imperfections allow the ceramic matrix to trap residues of the food contained in the vessels. The absorption of organic residues in glazed ceramics is demonstrated by analyses of modern vessels experimentally enriched with wine and vegetable oils (olive and lentisk oils) and archaeological vessels obtained from post-medieval Florence (Italy) and medieval Pla d’Almatà (Balaguer, Lleida, Spain). The analyses were conducted using gas chromatography–mass spectrometry following different extraction protocols aimed at identifying lipids and wine residues preserved in the ceramic vessels. Images of the glazed ceramic coating were recorded using an optical microscope and a scanning electron microscope to verify the presence of imperfections. In addition to providing information about the use of the studied vessels, the obtained results demonstrate how glazed ceramics can be studied to recover information regarding ceramic use and dietary practices in medieval and post-medieval periods when glazed wares were very common.