A half mirror has a shape on a substrate and excels in appearance and design and is fabricated by a method. The method includes forming an organic film by applying, onto a transparent substrate or film, a primer composition containing an addition-polymerizable compound having three or more reactive groups, an addition-polymerizable compound having an acidic group, and an addition-polymerizable compound having a hydrophilic functional group, and polymerizing the primer composition. The method includes turning the acidic group into a metal (M1) salt by treating the organic film with an aqueous solution containing metal (M1) ions, and turning the metal (M1) salt into a metal (M2) salt by treating the organic film with a metal (M2) ion aqueous solution containing metal (M2) ions that are lower in ionization tendency than metal (M1) ions, and (d) reducing metal (M2) ions to form a metal film on a surface of the organic film.