A method of producing a security document or article including a substrate (100), which is transparent at least to visible light, and a diffractive optical
microstructure (112). The method includes applying an opacifying layer (102) to at least one surface of the transparent substrate (100). An area of the opacifying layer (102) is exposed to
laser radiation (108) to ablate apertures (110) in selected portions of the opacifying layer (102), thereby forming a diffractive optical
microstructure (112) on the surface of the substrate (100). The
laser radiation may be patterned prior to exposing the opacifying layer (102), for example by passing the
radiation through a
mask (104). Alternatively, a focussed or collimated
laser beam (206) may be directed onto the selected portions of the opacifying layer (102).
Laser radiation may be directed onto the opacifying layer (102) either directly, or through the transparent substrate (100). Security documents or articles made in accordance with the method are also provided.