The desalting treatment was carried out on a Campanian ceramic dish, which was commonly used in ancient Greece as a daily necessity, by an immersion method. The conductivity of the leached solution was measured, and the ions present in the solution were analysed using ion chromatography. The conductivity of the leached solution gradually increased, reaching a value of 3,000 μS/cm after the ceramic dish had been immersed in it for 50 hours. Then, the conductivity showed an almost constant value of 3,000-3,100 μS/cm. The results of ion chromatography revealed that the leached solution contained Cl−, Na+, SO4 2−, Mg2+, Ca2+, and K+ ions. This result shows that these ions were extracted from chloride and sulfate, which had precipitated in the ceramic dish. As the Campanian ceramic dish studied here is believed to have been salvaged from a sunken ship, it can be inferred that the salts NaCl, KCl, MgCl2, MgSO4, and CaSO4 were present in the ceramic dish, indicating the salt components in the seawater. The relationship between the concentrations of each ion in the leached solution and the immersion time was examined. It was found that chloride from the ceramic dish was easily dissolved in water, whereas sulfate was not easily leached from the dish with immersion. This result indicates the difference in solubility of sulfate and chloride ions present in the ceramic dish when immersed in water. The ratio of SO4 2− to Cl− in the leached solution increases with the immersion time, implying a change in the dissolution rate of sulfate relative to chloride. Consequently, it was considered that the concentration of sulfate became high in the inner part of the ceramic dish and that of chloride became high near the surface of the dish through the process of salt weathering.
