Cheng Hanping shows one of the antique masks, regarded as sacred artifacts in Nuo Opera. Zhang Zixuan / China Daily

"The masks are the key of the Nuo culture," says Cheng, who has been pursuing the art form for 30 years. "Without masks, we are humans; putting them on, we are spirits and gods."

Cheng carefully safeguards four antique masks, including a gilt-bronze one bestowed by an emperor to one of his predecessors.

Younger-generation inheritors like Cheng worry about money.

"A new wood-carved mask costs 800 yuan ($131); we can't afford to make as many as we need," says the troupe leader, adding that the antique costumes they wear are becoming old and worn but they do not have the money for tailored hand-embroidered new ones.

The masks were once kept in the house of Cheng's senior fellow apprentice Cheng Fu-bao. In 2011, a fire destroyed his entire house, except for the four masks-the first and only objects the elder Cheng rescued.

"Unlike Western Halloween, the Nuo masks are sacred artifacts that have nothing to do with entertainment," says China Nuo Opera Research Institute's deputy director Wu Yunming.

The institute was founded in 1988 to preserve the culture of Nuo. More than 10 international symposiums on Nuo Opera have been held and about 20 volumes of books and paper compilations have been published.