which may be reversible so as to produce coloring and bleaching of the electrochromic material due to high corrosion resistance of such material the ion source may conveniently be a hydrous electrolyte application_number US 1338579 A description the figure shows first substrate 11 first contact layer 12 electrochromic layer 13 second substrate 14 second contact layer 15 spacer 16 liquid electrolyte 17 which is sealed between layers 13 and 15 by means of adhesive sealant 18 and source of direct current voltage 19 which is electrically connected to layers 12 and 15 via switch 20 according to the invention layer 13 consists essentially of a single crystal or polycrystalline tungsten niobate which is approximately represented by the formula w 9 nb 8 o 47 device manufacture devices of the invention may be manufactured e g by layer deposition on substrates fused silica and sapphire being among exemplary substrate materials both substrates may be transparent as e g in projection devices alternatively one substrate may be opaque as e g in devices utilizing reflected light substrates may serve to support contact and electrochromic layers and to contain a preferably liquid electrolyte ion source having the consistency of a solid paste or gel being alternatives to a liquid electrolyte prior to deposition of contact layers 12 and 15 substrates 11 and 14 are preferably polished and cleaned to enhance adhesion of contact layers among suitable transparent contact materials are doped semiconducting tin oxide and indium tin oxide which may conveniently be deposited by sputtering contact layers may also be made by depositing thin layers of ag au or pt by thermal or electron evaporation choice of preferred contact layer material being generally based on degree of transparency or reflectivity respectively depending on whether a device is intended.