Forefront of Senko-Hanabi Research

Abstract

A traditional Japanese sparkler, called Senko-hanabi, has been popular in Japan since the Edo-period. The simple composition of only 0.1 g black powder wrapped in a twisted paper generates a residue suspended at the bottom end of the paper string, emitting light streaks similar to branched pine needles, with ever smaller ramifications. The surprising events involve an exothermic reaction with the oxygen of air, chemical reactions of metastable compounds in the melt, gas bubble nucleation and bursting, liquid ligaments and droplets formation, all occurring in the sequential fashion. These complex processes at play in fireworks have remained elusive over the centuries. In this article, we introduce the research history on the science of Senko-hanabi starting from the 19th century, originated in Europe and then took place in Japan. We show the recent progress of the detailed cascade occurring at the spark ramifications as successive droplet fragmentation, thus answering a century old question. However, there still remain essential matters, which should be clarified in the future for the full understanding of the fragile beauty.