The girl used soybeans and water for this.
Japanese student Eimi Haga received the highest rating for ninja history, writing an essay in invisible ink. This was reported by the BBC.
The incident occurred at the Japanese National University of Mie. The freshman used the “aburidashi” technique. She crushed soybeans and mixed soybean extract with water to make ink. With their help, the girl wrote an essay. In fact, Haga handed a blank sheet of paper to Professor Yuji Yamada, but to prevent him from throwing out her work, she attached a note to the sheet to ‘heat the paper’. The teacher saw her notes and he heated the paper over a gas stove.
A student said that since childhood she was interested in a ninja. She learned about the technique of applying invisible ink from a book that she read as a child.
When the professor said in class that he would give a high mark for creativity, I decided that I would make my essay stand out from others. I gave a thought for a while, and hit upon the idea of aburidashi.Eimi Haga
Student of the Japanese National University of Mie
Professor Yamada praised the student and noted that he had never met an essay written using the Aburidashi technique. He noted that he did not hesitate to give the girl the highest rating without having read the work to the end. The man explained that he didn’t specifically heated the whole paper to save a sample for the media if they were interested in this case.