Analysis suggests 'Ming map' is authentic
Mr Liu said the map had been subject to accelerator mass spectrometry dating in tests in Singapore and the results showed it was probably drawn between 1730 and 1800. He said his map was drawn by Mo Yitong in 1763 and was a copy of Zheng's 1418 map.
Also defending the map in Beijing yesterday were Gavin Menzies, author of 1421 - The Year China Discovered the World, and Gunnar Thompson, director of the New World Discovery Institute in Washington.
Mr Liu contacted Mr Menzies and Dr Thompson via e-mail to take part in his research into the map after he was snubbed by historians on the mainland.
Mr Menzies admitted he had some initial reservations about the map because of the controversy. "I looked through all those things that've been mentioned as possible concerns and I found there is no reason to believe they aren't all authentic to the original," he said.
Mr Liu said he had not expected the controversy. "But the more people can take a good look at the map without prejudice, the more they will realise it can't be false."
The intellectual property rights lawyer has said he bought the map in a Shanghai bookshop in 2001. If authentic, the document may prove that Zheng and his crew circumnavigated the globe and discovered the Americas well before Columbus ever set sail.
However, Geoff Wade, a senior research fellow at the National University of Singapore's Asia Research Institute, who has studied Ming dynasty foreign relations for 20 years, last night stood by his earlier conclusion that the map was a "21st century forgery".
"It's an old piece of paper from somewhere. It's a paper that got tested and came back as an 18th century piece of paper. You can easily find old paper around. But it doesn't prove anything about the map. It's the content of the map which show it's been completely fabricated in the last five years," said Dr Wade, who has studied the map online.
He said he could give 20 reasons why the map was a forgery. One example was the use of simplified characters which would not have been used on an official map presented to the emperor. "Why do you want to prove it's real when every scholar in China who has looked at it has said it's a fake?"
James Qian Jiang, from the University of Hong Kong's Centre of Asian Studies who has studied Chinese maritime history for 26 years, said Mr Liu was misleading the public. "We academics are angry because everybody is being cheated," he said.