Lyu Xiaowei / Xinhua

Yet at the same time, Zao, who became a French citizen in 1964, was bound by two traditions, and this duality made his work stand out: a modernist style inflected with his understanding of traditional Chinese calligraphy, brushwork and landscape painting.

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"There was nothing like this contemporaneously taking place in China," says Sotheby's Branczik. "There was not the possibility for an artist to be painting freely and creatively in this way. So it could only have happened outside of China."

Given such a finite number of Chinese artists active in the 20th century, plus such a small pool of available artworks, it's no wonder prices are at the multimillion-dollar levels they are today. Branczik, who has spent much time in Asia with Sotheby's, is not at all surprised.

Instead, he says: "I think people who bought these paintings for next to nothing, and had them on their walls for two decades, insuring them for next to nothing, and then to have a Sotheby's expert come to their house and say, actually, 'This is a $6 million painting'-then there is definitely a lot of surprise."

Ming Liu is a journalist for the Financial Times.