I have a couple of small terracotta warriors in my apartment, acquired in Xi'an, near where the terracotta army of Emperor Qin Shihuang was discovered in 1974. The dried, yellow clay embedded in the folds of their armour makes them look quite authentic.
Small factories in Xi'an turn out thousands of warrior models every day, from miniature to lifesize, and the final stage of the process is rubbing in local clay for that authentic look. Only the most gullible tourist would be fooled.
Making reproductions look like the real thing has, however, become big business for counterfeiters in China who target not tourists but international art dealers and buyers. Copies of 2,000-year-old pottery soldiers and horses are now being produced in southern China with such skill that they pass sophisticated dating tests.
Measuring the radiation level, for example, established when an object was fired in a kiln, but the use of ancient pottery shards and clay in fake artefacts means the test now only authenticates the age of the material, not of the artefact itself.
Of much greater concern to the Chinese authorities is the smuggling out of the country of genuine antiques, many of which turn up in dealers' shops in Hong Kong's Hollywood Road. When national treasures are offered for sale which were looted by occupying powers during China's period of humiliation in the 19th century, that is a different matter again.
Four of these came up for auction in Hong Kong last week: a hexagonal ceramic vase commissioned by a Qing Dynasty emperor in 1743, and three bronze animal heads, all stolen from the Summer Palace in Beijing by British and French soldiers in 1860 in a war to force China to accept the opium trade.
Chinese authorities protested at the auctions, conducted by Sotheby's and Christie's, but a potential confrontation was defused when the three animal heads were bought for $4 million by the Poly Group, a Chinese corporation specialising in real estate which has a small antiquities museum in Beijing, and the vase for $2.7 million by the Beijing Cultural Relics Company.
China was embarrassed by the sale of its own stolen riches taking place in Hong Kong, which is now a Chinese city but with its own laws. But the affair highlighted a wider issue with international implications, underlined by an official at the relics bureau in Beijing who said international precedent and law dictated that art treasures looted in war time must be returned.
The right of ownership is often complex, tied up in history and politics, and is often a cause of international dispute. The true entitlement to the Elgin marbles, "acquired" by a 19th century British adventurer in Athens, is the subject of acrimonious dispute between Greece and the UK. The ownership of the 106 carat Koh-i-Noor diamond, taken by the British in 1849 and now part of the Crown Jewels, is a matter of contention with both India and Pakistan.
Campaigners in Wales would like to see the return of the 8th century Saint Teilo Gospels from the English cathedral which has kept them for 1,000 years. Glasgow last year returned the Lakota Ghost Dance Shirt, taken from a fallen warrior at the Battle of Wounded Knee in 1890, after a lengthy campaign for its repatriation. The return of Nazi loot from art galleries is a major problem for Jewish leaders.
Securing the return of lost national treasures was not a big issue in China as it struggled with invasion and wars. Most of the imperial valuables - 700,000 artefacts in total - were carted off to Taiwan by the defeated Nationalist army in 1949 and are now in the National Palace Museum in Taipei, in principle still part of China. Then, in the Cultural Revolution of 1966-1976, priceless objects were smashed throughout China by Red Guards in a campaign against feudal and imperial culture.
But these are different times. After years of relative stability and prosperity, China is beginning to take stock of the countless pieces which have left the country during and since the Opium War. Many grace museums throughout the world. Chinese objects acquired under the laws of the time or purchased from governments or individuals, such as those on display in the Chester Beatty Library in Dublin, are not a matter of dispute. But auction houses will have to think twice now about offering purloined Chinese artefacts in future, especially in Hong Kong.
Paradoxically, the trade in Chinese art is likely to benefit China. Chinese museums clearly now have sufficiently deep pockets to enter the market aggressively to buy back what they want.
Meanwhile, China is still immensely rich in ancient treasures, many yet to be uncovered. The terracotta warriors of Xi'an stand guard over unopened tombs containing thousands of priceless artefacts such as bronze chariots and horses which will take many years to excavate. I might buy one myself in the future, but only if it has authentic clay sticking to it.