method of marking a surface of an object by means of a laser light beam . a description is given of a method of decorating or marking , for example , synthetic resin objects by means of an uv - laser or ir - laser by coating the object with a layer of a dye precursor and a coupler in a binder . for the precursor use is made of a heterocyclic mono - or bis - arylsulphonylhydrazone and for the coupler use is made of , for example , an indole , aniline , pyrazoline or malonitrile , so that after irradiation with uv - laser light or ir - laser light an azo - dye is formed .