Cao wrote another book in his later years that compiled the kite-making techniques of both southern and northern China, recording the skills of kite making and flying, using mnemonic rhymes and illustrations to help readers understand and remember these techniques.
"When Cao wrote the book, his main wish was to help people with disabilities or otherwise struggling financially to acquire a skill, so they could support themselves," says Miao Bogang, 43, a representative inheritor of "Cao's kites".
The book, however, was only privately collected and withdrawn from circulation until 1943, when Kong Xiangze, who was then a student of painting and sculpture, was assigned by his teacher to transcribe a borrowed manuscript, which turned out to be Cao's work on kites.
Due to time limits, Kong only managed to make records of 14 of the 43 varieties in the book, and later spent decades working on restoring and refining these techniques, which he named "Cao's kites".