A gas purging plug for blowing gas into a metallurgical vessel, having the form of an elongated body made of a first refractory material, contains a final visual wear indicator in the form of an elongated core extending from an inlet end to a distance, along a central longitudinal axis, less than the length of the elongated body. The final visual wear indicator is made of a second refractory material that differs in visual appearance from the first refractory material between 800 and 1500 degrees C. The plug also contains an intermediate visual wear indicator extending from the inlet end to a point between the end of the final visual wear indicator and the opposite end of the elongated body. The intermediate visual wear indicator is made of a third refractory material that differs in visual appearance from the first and second refractory materials between 800 and 1500 degrees C.