March 16 (Bloomberg) -- Guy Ullens, founder of Beijing¡¯s largest private art museum, plans to sell a 900-year-old painting by one of China¡¯s most artistically gifted monarchs, as he trims his collection to raise funds, his auctioneer said. ¡°Rare Birds Sketched from Nature,¡± a 5.25-meter (17 feet) long ink scroll painted by the Song Dynasty¡¯s Huizong emperor (1082-1135), is the top draw in Poly International Auction Co.¡¯s sale of part of the Ullens collection, the auctioneer said today in a statement. The scroll, bought in 2002 for 23 million yuan, or $2.78 million at the exchange rate then, bears the seal of Qing Dynasty¡¯s Qianlong emperor, a sign that it once belonged in the imperial art collection. Ullens, scion of a family of Belgian diplomats and sugar industrialists, last month announced his plan to sell three pieces of work from one of the world¡¯s largest collection of Chinese contemporary art to fund his namesake private museum. Poly¡¯s auction, scheduled for May 25 in Beijing, will also include a dozen pieces from his collection of artwork from the Song, Yuan, Ming and Qing dynasties. Ullens, 74, began his collection with classical Chinese scrolls. As he began traveling frequently to China to run the family¡¯s sugar business in the mid 1980s, his interest expanded to contemporary Chinese art. The Guy & Myriam Ullens Foundation owns about 1,500 paintings, sculptures, installations and video works in its collection. They opened the Ullens Center for Contemporary Art in November 2007 in Beijing¡¯s 798 art district, housing their collection in a Bauhaus-style former arms factory. Chen, Zhang The Ullens wanted poly, China¡¯s largest auctioneer, to handle the sale to underscore his wish for his collection to remain in China. The Chinese government bans the export of most calligraphy, paintings produced before 1949. Even among artists who produced after the founding of the People¡¯s Republic 60 years ago, most major works are banned from exports. Chen Yifei¡¯s ¡°Thinking of History from His Space,¡± a 3.5- meter oil painting depicting the late artist pensive before a collage of Chinese history, will be on sale at Poly. Ullens said the painting was his favorite out of more than 90 pieces on display in the couple¡¯s July 2008 ¡°Our Future¡± exhibition. Ullens and his wife Myriam bought 15 pieces of Chinese contemporary art last year, including an Ai Weiwei chandelier for $657,000 from Sotheby¡¯s sale of Asian art in New York. Their collection includes paintings by Zhang Xiaogang, Zeng Fanzhi and Wang Guangyi. The Beijing-based auctioneer said price estimates for the works by Huizong, Zhang, and Chen are upon request. Fu Baoshi¡¯s ¡°Orchid Pavilion¡± will be on offer for an estimated price of between 1.8 million and 2.8 million yuan ($263,200 to $409,400), Poly said. The 2.3-meter scroll depicts Eastern Jin Dynasty calligrapher Wang Xizhi and his friends drinking wine and reciting poetry at the Orchid Pavilion. Paintings by Fu, who died in 1965, are forbidden by China¡¯s cultural bureau from being taken out of the country.