It has been found that negatively charged photovoltaic latent images, induced in zinc oxide binder layers at exposures higher than 10⁶ erg/cm², are not destroyed in water and the magnitude of its negative photoltage increases by the procedure of wetting with water. The electron latent images can be developed with a hydrophilic colloid developer, consisting of a dye and micellar colloid in water. The micellar colloid particles having a positive charge deposited on the exposed portions of zinc oxide binder layer. However, polymer colloid developers were ineffective for developing the photovoltaic latent images. The colloid materials capable of developing the latent electron image were organic acids such as tannic acid, aspartic acid, stearate chromic chloride, etc., and metal hydroxides such as aluminum hydroxide, iron (III) hydroxide, etc. The maximum density of 1.6 was attained with a developer consisting of stearate chromic chloride, water blue acid dye and water, and the image contrast was very high.