Following the 1966 flood in Florence, Italy, art conservators and scientists gathered to rescue many damaged works of art. Among the treatments developed at that time is a way to reverse the degradation of frescoes in which calcium carbonate has turned into calcium sulfate. The method used to reverse this change involved ammonium carbonate which attacks the gypsum crystals and turns them into CaCO₃. Conservators defeated microorganisms with Nystatin. Frescoes saturated with water were sealed with tributylphosphate (TBP) which prevented the frescoes from being washed away as the water evaporated.