"Usually, collectors who have focused on Chinese art for decades can appreciate the beauty of rubbings. It's difficult to enter this field suddenly," Song explains.

The calligraphy rubbings were appreciated by royals, officials and scholars in imperial China. It took knowledge of Chinese literature and calligraphy to understand them.

Jin Yunchang, a researcher with the Palace Museum, says Ellsworth's collections cover typical calligraphy works that span from the Qin Dynasty (221-206 BC) to the Song Dynasty (960-1279).

When these volumes were exhibited at the Palace Museum in 1996, museum officials had talked to Ellsworth about their desire to buy some of the rubbings for the museum from him. The connoisseur and art dealer had asked the museum to exchange them with some of its antique jewelry. The museum refused.

In 2003, after many rounds of negotiations with Ellsworth, the Shanghai Museum got four volumes from the collection at a record price of $4.5 million. The four volumes are part of Chunhuage Tie, the most-significant rubbings in Chinese history that cover more than 103 public figures' works, including pieces by emperors, master calligraphers and officials. They are now on display at the Shanghai Museum.

As for the remaining 11 volumes to be auctioned in late November, Song says the seller wants to sell them as a whole set instead of giving them to different people. The seller's identity remains a secret.

"We can't give an estimated price. It must be a huge sum," says Song.

She adds that a single book of rubbings dating to the Song Dynasty can cost millions of yuan based on previous auctions. The Ellsworth collection has seven dating back to the Song era.

"It's more than the price. The person who owns it can become a leading collector of rubbings."