Abstract: A generally non-transparent substrate is rendered substantially transparent, for example at a particular location or locations thereon, by electrostatically depositing finely divided transparentizing particles onto the substrate and then heating those particles to facilitate their flow into the intersticies of the substrate. The transparentizing particles have an optical refractive index that is substantially the same as that of the substrate, and these transparentizing particles have a melting point greater than that encountered during handling and storage and less than the temperature at which the substrate would be damaged.