NOVELTY - The method comprises preparing an aqueous mixture of a hydrogen sensitive pigment to form a first mixture, preparing a stable colloidal solution of metal activator nano-particles (3) by adding a water-soluble protective polymer to an aqueous solution of a metal precursor and by reducing the metal precursor with sodium borohydride to form a second mixture, adding the stable colloidal solution of the metal activator nano-particles of second mixture to the aqueous mixture of the hydrogen sensitive pigment to form a third mixture, and soaking a porous substrate in third mixture.    USE - The method is useful for forming a visual or chemochromic hydrogen detector for detecting hydrogen leakage or the presence of hydrogen in a confined environment such as room, car cabin and space shuttle cabin, where the hydrogen is useful: in fuel cells and liquid hydrogen fuel; for aerospace and transportation; and for hydrogen plants, oil refineries, ammonia plants, hydrogen reformers, fuel cell plants, chemical and analytical laboratories, nuclear power stations, hydrogen tanks, cryogenic storage systems and hydrogen-fueled vehicles.    ADVANTAGE - The method ensures simple and economic formation of the hydrogen detector with high durability, specificity and sensitivity, variable or tunable color reversibility and increased resistance to chemical degradation and without requiring specialized equipment such as vacuum vapor deposition apparatus, sputtering and electrophoretic devices.    DETAILED DESCRIPTION - The method comprises preparing an aqueous mixture of a hydrogen sensitive pigment to form a first mixture, preparing a stable colloidal solution of metal activator nano-particles (3) by adding a water-soluble protective polymer to an aqueous solution of a metal precursor and by reducing the metal precursor with sodium borohydride to form a second mixture, adding the stable colloidal solution of the metal activator nano-particles of second mixture to the aqueous mixture of the hydrogen sensitive pigment to form a third mixture, soaking a porous substrate in third mixture comprising a stable colloidal solution of metal activator particles and aqueous mixture of hydrogen sensitive pigment, removing the soaked porous substrate from the third mixture, and drying the porous substrate to form a visual hydrogen detector with reversible color change. The porous substrate is a fibrous structure (1) consisting of fabric, fiberglass tape, fiberglass cloth, glass fiber filter, filter paper, paper towel, synthetic paper, adhesive-backed fibrous materials, porous polymers and synthetic fiber fabric. The method further comprises treating the porous substrate with an aqueous suspension of the hydrogen sensitive pigment and the metal activator particles, and exposing the treated porous substrate to ultrasonic action to aid in penetrating the aqueous suspension of particles deep into the porous structure of the substrate material.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a fibrous material with micro-particles of a hydrogen-sensing pigment.    Fibrous substrate (1)    Hydrogen-sensitive pigment particles (2)    Metal activator particles (3)    Hydrogen gas. (4)