Zhang struggled to get Pu to sell him the piece as the man had previously sold Tang Dynasty (618-907) painter Han Gan's noted work Night-Shining White to a dealer, who later took it abroad. It is now in the collection of the Metropolitan Museum of Art in New York.

Zhang offered Pu a great sum of money to buy Pingfu Tie in 1937.

Among the other prominent works donated by the couple is Stroll About in Spring, a color painting on silk attributed to Sui Dynasty (581-618) artist Zhan Ziqian.

Zhang sold a courtyard that he owned in Beijing to raise money for it in 1945.

How passionate Zhang was about his art can be seen from an incident when he was kidnapped in Shanghai in 1941.

He told his wife that he would rather die than be freed at the expense of his art collection.

Pan was a loyal supporter of Zhang when it came to collecting art. And she sold her jewelry and other personal belongings to help finance his acquisitions.

Also, when the family was escaping from the Japanese during the wartime, she sewed the artworks into clothes to protect them.

The couple donated more than 100 works to the country after the founding of the People's Republic of China in 1949 and declined compensation of 200,000 yuan ($29,000).

Zhang Chuancai, Zhang's daughter, who is in her 80s now, says: "People didn't understand why my father sold his house, exchanged it for a piece of art and donated it. But I understand him.

"He loved his country. He believed these artworks should belong to his nation. And he would do whatever it took to keep them at home."