So whom does the 'Isabella' bust depict, and where did the artwork come from?

Prior to 1910, when she appears in the inventory of an art dealer in Florence, nothing is known about the terra cotta bust -- not whose likeness she captures, who created her or when. She is known simply as Bust of a Woman.

The dealer, Luigi Grassi, labels her from the Lombard School, a northern Italian art style from the eighth to 16th centuries. She was bought from Grassi sometime over the next two decades by Dr. Otto Lanz, a Swiss surgeon who lived in Amsterdam, and the bust was in his collection by 1931.

For a few years, art historians thought she might be by Leonardo da Vinci, as there is a profile sketch by da Vinci of Isabella d'Este, the Marchioness of Mantua and avid art patron, in the Musée du Louvre in Paris that resembles the bust. But there is no record of da Vinci making a terra cotta of d'Este. That attribution was short-lived, but the resemblance to known artworks of Isabella kept that portion of her identification alive.

There is a record from 1491 of d'Este commissioning Gian Cristoforo Romano, a multitasking artist, courtier, singer, poet and antiquarian, to create a marble portrait bust of her, although there is no record of that having been made. At best it is assumed that this is a terra cotta by Romano of d'Este from around 1500, and the only sure thing in that equation is the date -- give or take about 100 years -- as a thermoluminescence test performed in 1973 ascertained that the piece was made c. 1408-1538.

It is a Renaissance-era terra cotta. Where it came from before 1910 is still a cold trail, and the attributions to Romano aren't solid.

Isabella's journey

1910-12: The portrait bust of a woman shows up in the inventory of Florence art dealer Luigi Grassi.

1931: Dr. Otto Lanz (1865-1935), a Swiss surgeon living in Amsterdam, purchases the bust and it is in his collection by 1931.

1941: Lanz's widow, Ann Theresia Willi Lanz, sells her husband's collection to Hans Posse, Adolf Hitler's middleman, for 2 million Swiss francs and 350,000 Dutch guilders, "a big price but not a great price," says Kimbell curator and historian Nancy Edwards. The bust is transferred to the Kremsmünster, a collection spot where bought and stolen artworks are vetted for Hitler's planned Führer museum. The bust is deemed suitable and is sent to the Altaussee salt mine in Austria (one of several mines used for storing artworks), where it joins more than 6,000 priceless objects, including works by da Vinci, Vermeer and Michelangelo.

1945: Allied forces find the trove in the Austrian salt mine and hastily move everything to Munich, where they begin the arduous task of identifying the works and returning them to their countries of origin.

1946: Isabella is repatriated to the Netherlands Art Property Foundation in Amsterdam.

1951: The foundation decides that the Lanz collection was sold willingly to Hitler, and therefore will not be returned to the family. The Lanz works are sold at auction. The bust is purchased for 35 guilders (then about $10) by Lanz's daughter, Anna Gertrud Lanz Kijzer, who gives it to her brother Dr. Adrian Berchtold Lanz.

1973: Purchased by the Thyssen-Bornemisza Collection, Lugano, Switzerland, from Dr. Adrian Lanz through dealer Marco Grassi.

2002: Purchased by London art dealer Daniel Katz.

2004: Purchased by the Kimbell Art Foundation, for a reported $7 million.

-- Gaile Robinson