Sparks emitted from the sparklers or the ground iron rods are luminous owing to the phenomenon of heat radiation. Hence, the colors of these sparks change depending on the temperature according to Planck’s law. However, the mechanism of determining the temperature has not been clearly explained in a quantitative sense. Therefore, in the present study, we investigate two types of sparks, senko-hanabi, a traditionally popular Japanese sparkler, and ground iron spark, a well-known metal spark, using the two-color temperature radiometry technique and a theoretical analysis on heat balance. The temperature measurement clarifies that the temperature of sparks in a senko-hanabi is lower than that in the ground iron. The reason is revealed by the theoretical analysis that the heat production on a single spark of senkohanabi is 40 mW, which is lower than that of iron spark as 50 mW, and the fusion of potassium sulfate consumes 40% of the heat produced on the sparks. We conclude that the fragile beauty of the senko-hanabi, attributed to the relatively low temperature, is realized by two factors, less heat production and the fusion of potassium sulfate.
firework, spark, senko-hanabi, iron, temperature measurement, heat balance