PURPOSE: To obtain a transparent material having interference color or opalescent color, by dipping a transparent material in a dispersion of amorphous silica spheres having uniform particle diameter thereby attaching a thin silica film having uniform thickness, to the material, and heating the material at a temperature below the damaging temperature of the transparent material and the thin film.

CONSTITUTION: A transparent material made of transparent glass or plastic is dipped in a dispersion of amorphous silica spheres having uniform particle diameter of ≤1μ to effect the deposition of a thin film having uniform thickness and composed of the sillica spheres, and the coated material is heated at a temperature above 70°C and below the damaging temperature of the transparent material and the thin film to obtain the objective transparent material having interference color or opalescent color. The dispersion of silica spheres can be prepared either by hydrolyzing a silicic acid ester in an ammoniacal alcohol, or by treating sodium silicate with an ion exchange resin and heat-treating the resultant silicic acid. When the thin film is composed of a monolayer of the silica spheres, the material has interference color, and when it is multilayer, the material exhibits opalescent color.