Solid‐State Reductive Electrochemistry of Lapis Lazuli/Ultramarine

The reductive electrochemistry of different ultramarine specimens in contact with aqueous electrolytes is studied using the voltammetry of immobilized particles. This electrochemistry can be described in terms of the cathodic processes involving the chromophore species, S 3 − , S 2 − entrapped into the cavities of the lazurite lattice. Such processes involve a peculiar proton plus metal cation ingress into the solid framework, showing codiffusion effects characterized by chronoamperometric measurements.