Raman investigation of the patina layers on Hungarian copper ingots from a fifteenth century shipwreck

We report results of the patina study of underwater archeological finding ofmedieval copper objects performed by means of the Raman and complementary spectroscopic techniques. The objects were found submerged in the sea as cargo part of the ship which sunk in the Gulf of Gdansk in 1408. The excavated collection consists of 230 oval ingots of the size and mass up to about 60 cm and 18 kg (total of 2 tons), respectively. In the Raman spectra of the strongly porous ingot encrustation, the bands corresponding to the main patina representatives such as cuprite (Cu2O), atacamite (Cu2(OH)3Cl) and chalcopyrite (CuFeS2), and also chalcocite (Cu2S) and covellite (CuS) are observed and confirmed by the elemental analysis. Raman bands located at 1473 cm1 and also at 909 and 511 cm1 are ascribed to the organic Ca-oxalate (whewellite, CaC2O4 ·H2O) in agreement with the infrared spectra and surface morphology observed in microscope images. The presence of S, C, Ca, and Fe revealed by the energy dispersive X-ray spectroscopy indicate on patina components resulting from reactions in the microbial environment in seawater and on contributions coming from iron bars, tar, and burnt remains which were also found in the excavated cargo. The results are consistent with literature data on copper ingots from Hungary traded along the south–north route in medieval Europe.