Different metal and dielectric films are studied as masking films for the fabrication of optical waveguide structures in glass substrates by double ion exchange. The metal (Al, Ti, and Pt) films with thickness 0.5–1.0 µ m and inorganic dielectric films ( SiO2, Si3N4, and Al3O3) with thickness 0.2–0.5 µ m have piercing defect densities higher than 2×102 cm-2 and are not suitable for masks. For the first time polyimide and high temperature silicon varnish films are proposed for masks, as no pinholes or other piercing defects are found in them. The advantage of the polyimide films is demonstrated by the preparation of thin film homogeneous refracting waveguide lenses free of any highly scattering centers.