As part of his research for the book, the 60-year-old author studied historical records, jade ware found at archeological sites and visited almost all the jade mines in the Kunlun Mountains over six years.
"I went into the mountains several times, and sometimes I had to stay there for a week at a time," says Yu. "Every trip was a real adventure."
In October 2014, when he was about to return from a pithead named Qijiakeng, it began to snow heavily. The rugged cliff path then quickly disappeared under a blanket of snow.
"The path was around 4,600 meters above sea level," says Yu.
With a sheer cliff on one side and an abyss on the other, Yu was nervous. And, at one point, he lost his footing and began to slide. But fortunately he was rescued by his companions.
"Such risks were quite common during my trips to the mines. We had to wade through rivers, climb cliffs and sleep in the open," says Yu.
In his book, he says that ziliao was not transported to the central plains until the middle of the Han Dynasty (202BC-220AD), as he did not find any jade ware made before that time from the Hotan material.
He also believes that Chinese did not mine jade in the Kunlun Mountains until the Ming Dynasty (1368-1644).
He also says that Zhang Qian (164-114BC), a man credited today with opening China's terrestrial Silk Road, was the pioneer when it came to bringing Xinjiang Hotan jade to the central plains.
