PURPOSE: To widen a temp. range holding viscosity necessary for forming a flow pattern, by using a visualized material containing silicone having viscosity of 105W106cst at 25°C and pigment in the flow detection of a fluid.

CONSTITUTION: A visualized material containing silicone having viscosity of 105W106cst at 25°C and pigment is used in the flow detection of a fluid. The silicone to be used has viscosity of 105W106cst at 25°C and, if below 105cst, the visualized material is easily deformed by the pressure of hydraulic oil and a visualized pattern having a length equal to or more than a necessary degree is formed. If above 106cst, said material is not plastically deformed by the usual pressure of 2W5kg/cm2 of hydraulic oil and shearing force due to flow and no visualized pattern is obtained.