Rub a function in the pressure under, can appear the printing ink of color.Join special chemistry to try or change color material and make into in the printing ink.Use this kind of printing ink printing of there are color or invisible diagram text, when article or tool which be to use hard quality rub, press to press, then the occurrence is chemical of the pressure color change or the tiny capsule break dyestuff to show to leak and appear a color.(red, blue, green, purple, Huang etc.)Can request the choice shows according to the customer of the color also designs secret marking.