The Great Buddha at the Mogao grottoes, constructed during the Tang dynasty (618-906) and housed in the site's landmark pagoda. Photo: Guillermo Aldana.

A view of the cliff at Mogao. The nearly five hundred cave temples that remain at the site are carved into the face of the cliff. Photo: Neville Agnew.

The nine-story pagoda at the Mogao grottoes, which houses the Great Buddha sculpture from the Tang dynasty. Photo: Dusan Stulik.

A detail of a wall painting in Cave 85 of Buddha and bodhisattvas. The painting dates from the Tang dynasty. Photo: Sun Hong Cai, © Dunhuang Academy/J. Paul Getty Trust.

Interior view of Cave 23, with environmental monitoring equipment in place. Photo: Dusan Stulik.

Li Tie Chao (right), a Chinese member of the project team, performs color monitoring in one of the grottoes at Mogao in 1989. At left is Neville Agnew, then GCI Scientific Deputy Director. Photo: R. Tseng.

Project team members at the top of the Mogao cliff face examine the autonomous, low-maintenance environmental monitoring station designed by GCI staff. Photo: Martha Demas.

A portion of the synthetic textile windbreak fence, erected on the cliff above the caves, was designed to reduce sand accumulation at the site. Photo: Dusan Stulik.

The beginnings of the vegetation windbreak fence at the Mogao grottoes. This natural windbreak of desert-adapted trees and shrubs is intended to supplement and ultimately replace the synthetic textile fence. Photo: Po-Ming Lin.

The interior of Cave 61 at the Mogao grottoes, constructed in the 10th century during the Five Dynasties period. Photo: Guillermo Aldana.

A polychromed sculpture of Buddha in Cave 328, dating from the Tang dynasty. Photo: Guillermo Aldana.

The Colossal Buddha at the Yungang grottoes in Datong, China. The rock-carved figure is 60 feet in height. Photo: Guillermo Aldana.

An overview of the Yungang grottoes in 1988. Urbanization can be seen surrounding the site. Photo: Luis Monreal.

Exterior view of a portion of the grottoes. Sculpted decorations have eroded on the exposed facades. Photo: Guillermo Aldana.

View of polychrome sculptures in one of the Yungang grottoes. The project included analysis of paint samples to determine the nature of the original polychromy, its deterioration, and its present condition. Photo: Guillermo Aldana.

Close-up of a polychrome sculpture shows the extensive particulate coating on the sculpture. This is a consequence, at least in part, of coal industry activity in Datong. Photo: Guillermo Aldana.

Participants and instructors in the GCI's site management training course at the Yungang grottoes in 1992. The course was for senior grotto site managers from sites around China. Photo: Margaret MacLean.

Site management training course participants conduct a condition report in Cave 10 at Yungang. Photo: Margaret MacLean.

Project team members examine color pigments in Cave 6 in Yungang as part of the sculptural polychromy analysis. Photo: Po-Ming Lin.

Massive polychromed carved figure in Cave 13 is covered in a layer of particulate matter. Testing indicated that particle concentrations at Yungang were four to six times higher than those found in downtown Los Angeles. Photo: Guillermo Aldana.