The effects of nickel flashing on thermal-shock resistance of ceramic coating and mill additions of cobalt oxide on enamelling in nitrogen stream were studied from the points of interfacial microstructure proposed and adherence strength.The new method for measuring thermal-shock resistance of ceramic coating is that the coated specimens are heated for 5 min. at the specified constant temperature which is taken either as the maximum saftey-temperature for actual use, or (0.7-0.8)×(enamelling temperature 3°C), and rapidly cooled in water. These heating and cooling operations are repeated until the gain in weight by oxydation of base metal becomes comparable with loss by peeling off. Then the relation between the amounts of peeling of coated layer and times of repeating will be expressed by a curve which has asymptotic constant value of saturation. From this curve thermal-shock resistance, R(%), can be calculated by following formula.R(%)=Maxium amounts of peeling/Initial weights of coating layer×100%The resistance, is thought to be nearly proportional to the adherence strength at room temperature. However, the existence of ferrosilicate layers which develope at 850°C for 30 sec. on interface by prefiring of nickel flashed base metal. Also increases thermal-shock resistance. From this reason, it is considered the ferro-silicate layer whose thickness is about 2-3μ, acts as to decrease the maximum amount of stress occured in coating layer.The catalytic action of metallic nickel deposited by nickel flashing, being expressed by Fe3O4+Fe+Ni→4FeO+Ni, is promoted by acid etching after nickel flashing. Therefore, the kinds of acid and etching methods are important procedures for good enamelling.For firing in nitrogen stream, mill additions of cobalt oxide are effective to increase adherence strength and thermal-shock resistance. Most effective addition is 3% CoO. This is due to the fact that selective galvanic corrosion of CoO remarkably occurs at this content and this corrosion state can be seen by the micro-photographs of interface. (Fig. 12)When the galvanic corrosion of CoO and reducing action of nickel flashing simultaneously act during enamelling, these actions cancel each other so that both of thermal-shock resistance and adherence strength of specimen greatly decrease, in general.