The Palace Museum in Beijing held an eye-catching show in 1996 on rubbings of rare Chinese calligraphy works, titled Chunhuage Tie.

It was based on a collection of US connoisseur Robert H. Ellsworth, a legendary collector of Asian and Chinese art. The four volumes on show were among Ellsworth's 15 rare rubbing collections.

The four volumes were bought in 2003 by the Shanghai Museum at a price of $4.5 million, a worthy treasure, as experts called it, that fills in "some blanks in Chinese calligraphy history".

But no one knew where the rest of Ellsworth's collection was until China Guardian Auctions announced in Beijing earlier this month that it will go under the hammer at its autumn sale from Nov 20 to 24.

"I've heard of them for years. It's the first time I will see them. This is very exciting," says Zhao Liguang, a former director of Beilin Museum in Xi'an, Shaanxi province.

The museum focuses on steles.

Rubbings were very important for the preservation of calligraphy works before printing was invented during the Tang Dynasty (618-907). Works of many master calligraphers, such as Wang Xizhi and Wang Xianzhi, were appreciated by their followers only through rubbings left behind.

Zhao says rubbings are very valuable because many stones with inscriptions have already been destroyed or are hard to read today.

The 11 collections of rubbings from Ellsworth's trove comprise different types of calligraphy works, including two on works of Jin Dynasty (265-420) calligrapher Wang Xizhi, who is considered the greatest Chinese calligrapher in history.

According to Song Hao, general manger of the department for rare books, rubbings and manuscripts at China Guardian Auctions, all volumes were bought by the US collector between 1989 and 1995 from Christie's and Sotheby's in New York, and cost him more than $1.2 million.

"In terms of numbers, Ellsworth's collection of rubbings is not large. But the items are rare and well-known," says Song.

Song adds that it was rare for a foreign collector to show interest in rubbings when Chinese calligraphy was still difficult for them to appreciate. In fact, even the number of Chinese collectors of rubbings is small compared to those buying ink paintings and antiques today.