to the atmosphere in which the substrate contains an oxidizable metal compound having a color and a development speed under atmospheric conditions the method comprising the step of contacting the substrate with an oxidizer to increase the development speed of the color the substrate may be natural or manmade such as a hydraulic material for example concrete the oxidizer is preferably free of chromates the oxidizer is preferably applied to the substrate in an aqueous solution application_number US 6836302 A description in this patent document u201c comprising u201d means u201c including u201d and does not exclude other elements being present in addition a reference to an element by the indefinite article u201c a u201d does not exclude the possibility that more than one of the elements is present a substrate is any material having a surface that in use is exposed to viewing and that may be stained with a metal compound example of substrates are floors walls decks playground surfaces driveways sidewalks roadways paths paving stones tiles roofing tiles and architectural features such as countertops tables columns facades and statues substrates include man made materials for example blocks bricks concrete polymer modified concrete including overlays cementitious materials or other hydraulic materials and natural materials for example limestone marble and slate a hydraulic substrate is a substrate made.