Chinese experts said they have found the causes for the fading of color in the renowned frescos at Dunhuang Grottos in northwest China, denying ceruse oxygenation as the main cause as traditionally considered.

"Scientific analysis shows that the discolored part in Dunhuang frescos, mainly the color of skin, did not use ceruse at all," said Wu Rongjian, a research member with the art research branch of the Dunhuang Research Institute.

Analysis of pigments of Dunhuang frescos reveals three factors have contributed to the discoloring of portraits.

The factors include the use of red lead coloring, oxygenation of vegetal pigments and large quantities of alkaline elements, which catalyzed changes in pigments.

According to Wu, the discoloring of Dunhuang frescos has experienced two phases. From the Northern and Southern Dynasties (420-589) to the beginning of the Sui Dynasty (581-618), the flesh color and similar colors changed into black or leaden gray, and from the middle ages of the Dui Dynasty to the Yuan Dynasty (1271-1368), the color changed into brown.

As research shows, most pigments used in Dunhuang frescos are natural ore pigments, with vegetal pigments and man-made pigments also being used.

"Although some changes have taken place to flesh color in Dunhuang frescos, as most ore pigments are sustainable, Dunhuang frescos are still bright and fresh after thousands of years," said Wu.

Listed on the World Heritage List of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1987, Dunhuang Grottos in Gansu Province boast 40,000 cultural relics including manuscripts, paintings and musical instruments, covering the period from the fourth to the 11th century.

(Xinhua News Agency March 15, 2004)