PURPOSE: To form a bright optical pattern in a high pattern concentration, by exposing a porous glass material impregnated with a specific photo-setting composition to patterned light, removing the unhardened composition remaining in the unexposed part, and carbonizing the photoset composition.

CONSTITUTION: A porous glass material 1 is impreganted with a photo-setting composition containing one or more selected from the group of (meth)acrylic acid esters, derivatives thereof and acrylic acid esters and a photosensitizer as necessary, and exposed to light through a mask 2 having a desired pattern to photoset the composition impregnated into the exposed part 4-1. The unhardened composition present in the unexposed part 3-1 is removed from the glass material 1 by solvent treatment and the solvent is then removed by heating, etc. The glass material 1 is then heated to carbonize the photoset composition in pores. Thus, a part 4-2 is blackened, and a black pattern corresponding to the pattern of the exposure mask 2 can be formed in the porous glass material 1.