Since they were first unearthed 30 years ago, the terracotta warriors and horses of the Qin Dynasty (221-206 BC) have always appeared before the public with a dull, gray look.

Around 2,000 clay sculptures unearthed from the Mausoleum of Emperor Qin Shihuang (259-210 BC) were an amazing archaeological coup when diggers started the excavation in suburban Xi'an, the capital of Northwest China's Shaanxi Province, in 1974.

The impressive sculptures had lost much of their color in their two millennia underground, and the remaining colors are fading quickly from being exposed to the air.

One colorful terracotta warrior is making its debut outside Xi'an at an exhibition in Beijing on the application of science and technology in the protection of Chinese cultural relics.

The exhibition runs until October 25 at the Millennium Art Museum, China Millennium Monument.

This "warrior" has retained its looks in the 2,000 years underground, appearing more alive and muscular than his gray battle companions.

Visitors may well be captivated by the green face and fiery big eyes of the 1.6-metre-tall statue, who is kneeling on his left knee.

His face has been painted green because he either came from one of the non-Han tribes living in northern and western China, or because he needed to frighten his enemy.

Visitors can observe his thick, black eyebrows, black eyes staring ahead and the red cloth binding his hair. The chocolate-colored armor was thought to be made of shells connected by vermeil ribbons.

The warrior's firm hands reach out of his brown robe. The pose shows he was holding a bow and an arrow, which have broken into pieces.

It has taken Chinese and German researchers decades to find a way to preserve the colored drawings on the ancient terracotta.

Scientists discovered the craftsmen of 2,000 years ago applied one or two layers of Chinese raw lacquer on the surfaces of the sculptures and then painted them for decoration.

However, the "warriors" could not hold back time after the fall of the dynasty.

They have been damaged or even demolished, by both nature and humans, whilst buried and after excavation.

Besides signs of cave-ins, scientists have also discovered from this accompanying part of Qinshihuang's mausoleum signs of a fire, which caused the greatest damage to the terracotta and the drawings.

Historians have given the following three hypotheses for the fire.

Some said a shepherd started it by accident searching for goat using his flame torch.

Others believe in a legend about Xiang Yu (232-202 BC), the leader of armed rebels, who ordered his men to start a fire in the mausoleum area. Xiang and others rebelled against and overthrew the Qin empire largely because Qinshihuang had been considered -- as later described in historical documents -- a tyrant.

Another argument goes that setting fire to a tomb building was a funeral custom of the time.

Two millenniums later, the colored drawings on figurines were damaged by the atmosphere as they were excavated and exposed to daylight and electric lights and experienced a sudden change in temperature and humidity.

Both the layer of raw lacquer and the colors applied on it peel off in the humid open air, resulting in a gray look.

"The damage was caused partly because archaeologists cared more about how many sculptures were dredged up, than about preserving the colored drawings on a 'warrior' in the early phase of the excavation project on the mausoleum," said Wang Yudong, deputy director of the Millennium Art Museum, who is also an expert on the Qin terracotta warriors.

"As the project went on and international exchanges became frequent, people gradually realized the significance of protecting all the information attached to cultural relics in the mid-1990s," he added. The information includes drawings and colors on the Qin terracotta.

A major breakthrough was made in the 1990s when researchers from China and Germany co-invented a special kind of lotion, which binds the layers of color tightly to the sculptures.

Before cleaning the dust on the sculptures, scientists first inject the lotion into the sculptures' surface, while stripping off the dust bit by bit.

Once completed the sculptures are immediately moved to museums, where humidity is strictly controlled at a level of 50 per cent, with a temperature between 18 and 20 degrees Celsius.

The colored drawings remain weak even after treatment. There are still threats of color changing and fading, as a result of the oxidation.

Blue and green, the main colors of clay sculptures are most vulnerable. Pigments of the two colors contain minerals and plant ingredients which are easily oxidized.

Measures were taken to prevent the oxidization of ancient pigments applied to the "green-faced warrior" on display at the exhibition during the transportation of the rare relic, which is part of the collection of the Emperor Qin's Terracotta Museum, said Wang.

(China Daily October 19, 2004)