1. The present invention concerns a gas purging plug (1) for blowing gas into a metallurgical vessel comprising: 2. (a) An elongated body (2) made of a first refractory material and extending from a first, inlet end (2a) to a second, outlet end (2b) over a distance, H, measured along a central longitudinal axis (X1) comprising, 3. (b) At least one gas flow path (3) fluidly connecting a gas inlet (3a) located at said first inlet end of said elongated body to a gas outlet (3b), located at the opposite second, outlet end; 4. (c) A final visual wear indicator (5) in the form of an elongated core extending from the first inlet end (2a) to a first distance, h1, measured along the central longitudinal axis (X1), which is less than the length, H, of the elongated body, h1 < H, said final visual indicator being made of a second refractory material of different visual appearance than the first refractory material at least at a temperature comprised between 800 and 1500° C, Characterized in that, it further comprises an intermediate visual wear indicator (4), partially embedded in the final visual wear indicator (5) and extending from an initial distance, h0, to a final distance, h2, from the first, inlet end (2a), wherein h0 < h1 < h2 < H, and wherein the intermediate visual wear indicator (4) is made of a third material, permitting to yield a different visual appearance than the first and second refractory materials at least at a temperature comprised between 800 and 1500° C.