A Japanese student aced her assignment about ninja culture by making her own invisible ink from soybeans, a stealthy move that impressed her professor.
Eimi Haga, a 19-year-old member of Mie University’s ninja club, wrote an essay about a visit to a ninja museum with a message to her teacher. She told him to heat the essay before he tried to read it.
Yuji Yamada, who teaches Japanese history and ninja culture, took her essay home where he carefully heated it using a stove. When Haga’s essay revealed itself in the heat, Yamada, who promised his students extra marks for creativity, awarded her an A.
“She replicated what is written in records about ninja writing. She proved it actually works and she went through a trial-and-error process,” Yamada said.
Haga made the ink by soaking soybeans overnight and then squeezing them into a paste. She tested three different kinds of paper to find the best one.
“If the paper is too thin, it burns when heated. If it’s too thick, it doesn’t absorb the ink very well,” she said.
Yamada said when asked to be creative, his students usually presented their reports shaped as scrolls, or folded into throwing stars.
“We discussed the use of invisible ink, but I was amazed that someone actually used it,” he said, adding that he didn’t read the entire paper because he wanted to keep some of Haga’s work invisible.
“By learning about ninjas, we can apply their knowledge and ways to modern society,” Yamada said.