of chain polyamide molecules takes place by ultraviolet rays the photo setting resin solution used in the present invention of still another type is a hydrosol solution which is produced in a manner that bichromate or diazo compound is added to a colloidal solution of organic macromolecule such as gum arabic starch albumen gelatine and polyvinylalcohol the hydrosol solution thus produced is hardened by irradiation of ultraviolet rays a plasticizer elastic polymer and surfactant may be preferably added to the resin solution to the resin solution described above is added a dyestuff and or pigment to produce a coloring liquid and the coloring liquid is applied to the thread to be colored this is preferably done in such manner that the thread is passed between two layered porous material e g felt and sponge which has been soaked with the coloring liquid the thread with the coloring liquid thinly and uniformly coated thereon is thereafter subjected to irradation of ultraviolet rays wavelength of about 200 400 m u03bc for about 0 1 to 20 seconds a sterilizing lamp high pressure mercury lamp carbon arc lamp xenon lamp or the like may be used to produce ultraviolet rays the following examples describe the preferred manners and modes contemplated by the inventors for carrying out the method of the present invention however it is to be understood that the present invention is not limited to the following examples except as defined in the appended claims the coloring liquid was prepared by the following compositions and then applied to a nylon thread the nylon thread was then subjected to irradation of a high pressure mercury lamp for 5 seconds to harden the liquid thereby forming a colored film on the thread.