Thin films of Buckminsterfullerene exhibit a reversible electrochromic effect when electrochemically intercalated with alkali metal or alkali earth ions. The degree of reversibility depends on the ratio of intercalated ions to fullerene molecules, both in the bulk film thickness and in localized stoichiometric gradients. High ratios of ions to fullerenes product films with limited electrochromic reversibility. These films are also soluble in the polar organic electrolyte system, leading to cycling and durability issues. If the intercalating ion current is modulated, rather than continuously applied, improved durability and reversibility result. The relationship of stoichiometric gradients to intercalation ion current density and ion mobility in the fullerene film are considered, as are optimum pulse-widths. Film preparation and electrolyte preconditioning are detailed.