Possessing a lineage stretching back thousands of years, the ancient art of “liu li,” or Chinese colored-glass, is now facing looming extinction, as the traditional manufacturing of such cultural heirloom is deemed as a major cause of air pollution in the country’s capital.

Being praised as one of the top five Buddhism jewelries, liu li is famous for its complicated production process and beautiful luster. The vitreous artworks are extensively used on royal architectures and ornaments, while the most famous royal liu li factories have been thriving in Beijing’s Mentougou District for over 700 years.

Despite the cultural connotation it conveys, traditional liu li art is now facing an inevitable fate of extinction. According to Beijing Youth Daily, all factories producing liu li in Mentougou District have been shut down this year, as they may cause heavy air pollution.

“Our factory has stopped operations since April. The high temperatures produced by coal-burning kilns is crucial for making traditional liu li, but the practice has been banned by local authorities, because it causes air pollution,” Sun Hongli, manager of Guduguohua Liu Li Company in Mentougou District, Beijing, told Beijing Youth Daily.

According to Sun, his company has been providing liu li for many traditional museums and buildings, including the Forbidden City. But the recent ban has disrupted the company’s production plans, forcing him to rely on outside producers.

“The liu li making technique is quite different in other regions, while the earth needed to make perfect liu li only exists in Mentougou District, thus it’s really hard to produce liu li with good quality elsewhere,” said Sun.

In response to the incident, Beijing’s environmental protection authorities told Beijing Youth Daily that the liu li factories were forced to shut down because their coal-burning kilns pose a threat to the local environment, adding that it is still unclear when and if the factories can restart their operations.

“We know that liu li art is China’s intangible cultural heritage, and it’s a pity that the factories had to close. But in an effort to protect the environment, there was no alternative,” said an official, who added that the local government will try its best to protect the ancient art.