Abstract: An antireflective layer is formed on a surface of a body of phase separable glass by heat treating the glass to cause it to become separated into at least two distinct phases of different solubility. A surface of the body is subjected to a leaching solution which preferentially leaches at least the most soluble phase, leaving a surface layer consisting of a skeletal structure that comprises the least soluble phase. The leaching solution preferaby contains an acid which etches the skeletal structure which becomes so modified that the film exhibits an effective refractive index gradient thereacross, the film therefor exhibiting antireflectance properties over a wide band of wavelengths.