The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is extremely consistent, and it becomes a transparent gel from 350 to 850 nm (visible region). Moreover, voltammetry and chronoamperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a large variation of transmittance values (around 60%) when Cu2+ is added to the gel. It was also shown that copper cations promote Bi/Bi3+ reversibility by a redox reaction between Cu2+ and metallic bismuth. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis were used to verify possible changes in the gel when it was exposed to a heating/cooling cycle. From TG analysis it was possible to verify that degradation of the gel polymer in a large temperature range does not occur and from DSC it was observed that the system only freezes at ca. -35degreesC. (C) 2003 The Electrochemical Society.