Arecent report on the breaking of a stone lion's ear on the Marco Polo Bridge has aroused public attention on the protection of historical stone carvings and stone architecture against deteration by efflorescence.

The Beijing Evening News first reported that a small piece of the lion was deliberately broken off by a passerby during the night.

Further investigation by a team of experts on stone relic protection concluded it to be the result of efflorescence.

The Marco Polo Bridge, 'Lugouqiao' in Chinese, was built in 1192, spanning the Yongding River near the town of Wanping, 15 kilometres southwest of Beijing's centre.

Its English name came from the renowned Italian explorer Marco Polo, who travelled through and in China between 1275 and 1291. He depicted the bridge in his published diary as "a very fine stone bridge, so fine indeed, that it has very few equals in the world."

On July 7, 1937, the bridge featured again in Chinese history when the Japanese Kwantung Army declared war to conquer China. It is known as the "Marco Polo Bridge Incident."

The 498 stone carved lions crouch along both sides of the balustrade as a symbol of China's ancient stone carving skill and art.

Unlike other parts of the bridge, made of marble, the lions were carved on sandstone, according to Gao Nianzu, a retired authority in anti-efflorescence protection from the China Relic Protection Office.

"In ancient China, due to the limitation of tools, marbles were too hard to carve. People at that time used sandstone, softer to carve, but much more vulnerable to deteration," says the 76-year-old.

"The problem [of efflorescence] is universal, but the situation in China is becoming worse."

According to Gao, the process of efflorescence has been greatly quickened after the founding of New China in 1949.

Efflorescence is sulfur dioxide in the air attaching to water vapour contained in a stone to become corrosive sulfuric acid (H2SO4) which stays on the surface of the stone and erodes it. Its extreme case is when the acid evaporates in the air to fall with precipitation, commonly known as 'acid rain'.

"Though there is no report of acid rain in Beijing, there has been a remarkable increase of sulfur dioxide in the air in recent years, brought about by industrial air pollution," Gao says. "I am not exaggerating to say that if the problem is left untreated, it will bring a monumental loss of China's historical stone inscriptions and carvings within decades."

As an example, Gao cites, "About 90 years ago, a French photographer took a picture of the balustrade in front of the Taihe Hall in the Forbidden City, on which is carved a phoenix.

"From the picture, you can still see the exquisite carvings of the feather on the phoenix. Now, we joke sarcastically that the phoenix has become a roasted cock because you can not find any traces of the feather."

Although China started its anti-efflorescence project in 1981, the problem has not yet gained its deserved attention from either the government or the public.

"We have found a practical and economical way, namely the priming of silicone, to protect stone from further decay," he says. "However, its application is still far from extensive."

The Marco Polo Bridge is one of the few monuments that is protected by the silicone primer. Gao's constant observation of the results over the past dozen years has proved the silicone to be successful. However, it now needs to be reapplied.

"The recent minor damage of the lion is an invitation for another priming of silicone," he says. "For any relic preservation, maintenance msut be constant."