Electrochemistry of iron oxide pigments (earths) from pictorial microsamples attached to graphite-polyester composite electrodes

The electrochemical response of different iron pigments attached to graphite-polyester composite electrodes is described. Characteristic differential pulse voltammetric profiles were obtained for green earth, iron oxide red, Mars black, ochre yellow, Sienna raw, umber raw and Van Dyke brown. Proton-assisted reductive dissolution processes occur at the three-phase boundary of the substrate electrode-attached solid electrolyte solution system. Microsamples extracted from polychromed sculptures, canvas paintings, wall paintings, altarpieces and panel paintings from Spain, Ethiopia and Italy from the 12th to the 20th centuries were electrochemically identified in agreement with polarized light microscopy, SEM/EDX, XRD and FT-IR data.