Scaling of Fold, bronze, and stainless steel was investigated in synthetic fresh and seawater. It is shown that the calcium carbonate precipitation rate increased from stainless steel, to bronze and then to gold whatever the composition of the scaling water. The morphology of the deposited scale depended on the substrate and on its surface state. For fast scaling, as with 200 mg dm(-3) Ca2+ carbonically pure water, calcite was mainly deposited: for slower scaling vaterite was also observed. When foreign ions were added in the scaling water, aragonite appeared. In particular, for synthetic seawater, cc-here magnesium ions are highly concentrated, aragonite is preferentially selected, so at the end of scaling aragonite covered the whole electrode surface. The kinetic parameters, which characterize a precipitation model, were extracted from impedance measurements through a fitting procedure. The morphology of the precipitated calcium carbonate was examined by means of a scanning electron microscope.