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Desalting treatment by an immersion method was performed on an ancient Greek and Roman Terracotta statue of a person. The conductivity of the leached solution was measured, and the ions present in the solution were analysed by ion chromatography and titration with a sulfate solution for HCO3-. The conductivity of the leached solution increased rapidly after the Terracotta statue was immersed in it for 50h. Then, the conductivity showed a gradual increase, eventually remaining almost constant at 250 μS/cm. The analysis by ion chromatography and titration results revealed the presence of HCO3-, Na+, PO4³-, SO₄²-, K+, and Cl- in the leached solution, with the first three being the main constituents. The results showed that these ions were derived from the carbonate, phosphate, and subordinate amounts of sulfate and chloride precipitated from the Terracotta statue. The relationship between the concentrations of the aforementioned ions in the leached solution and the immersion time was examined. The time required for 50% dissolution of each ion in the leached salt from the Terracotta statue was estimated to determine the difference in dissolution rates between the leached ions. The estimated times for 50% dissolution of the ions were as follows: Na+, 39.5h; Cl-, 44.0h; K+, 55.2h; SO4 2-, 60.0h; PO4 3-, 97.0h. It was, therefore, concluded that phosphate from the Terracotta statue dissolved to a much lesser extent in water than did sulfate, which did not leach out readily; this behaviour could explain the low solubility of phosphate in water.
Research papers (publications of university or research institution)
