The present invention employs zinc powder and a vehicle containing an aqueous solution containing a specific alkali silicate, an ammonium ion, and a halide ion at specific concentrations; a vehicle containing an aqueous solution containing the above ingredients at specific concentrations and additionally an alkali halide at a specific concentration; or a vehicle containing an aqueous solution containing a specific alkali silicate and an alkali halide at specific concentrations, wherein the vehicle and zinc powder are contained at a specific ratio.
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