Another promotion of a non-Leonardo, pushed by the Corriere della Serra, which has been a great newspaper. I was contacted by someone called ********** (removed at the request of the editor) - not, apparently, an accredited arts journalist. I declined to express a visual opinion on the basis of the poor reproductions I had seen but made it clear that any attribution to Leonardo was not consistent with the documentation. The result is that I am implicitly cited as a supporter of the attribution. I will be asking for a retraction. (note: they subsequently published an accurate interview with Francesca Pini, a very good arts journalist)
Having looked further at this, it is clear that the painting cannot be by Leonardo, on the basis of the documented account of Leonardo's relations with Isabella d'Este and his evident failure to paint her portrait. The documentation (in summary) runs as follows:
1) Leonardo made a finished drawing of Isabella when he was in Mantua in 1500. He left this behind in Mantua but Isabella's husband, Francesco Gonzaga, gave it away, much to her irritation. This is almost certainly the autograph cartoon partly coloured in chalk in the Louvre, which is pricked for transfer.
2) The studio made a revised version of the cartoon to take away with them (now in the Ashmolean Mus in Oxford), which was seen when Leonardo visited Venice. This was made from the Louvre cartoon, as the sploveri (dots of charcoal) confirm. The original cartoon has been revised to give more adequate room for the sitter's right arm, which is lowered, together with the ledge on which is rests and the book to which she points. The revised cartoon was taken back to Florence so that Leonardo could potentially make a painted version.
3) When Leonardo was back in Florence Isabella pestered him for 6 years for a painted version of the portrait or for any painting from his hand.
4) The correspondence suggests that she was not successful.
5) If Leonardo or the studio produced a portrait it would have been based on the revised version that they had with them not the one Alfonso had given away.
6) At some point the Louvre cartoon was cut down, with the loss of the ledge and book. This makes nonsense of her pointing gesture. The painting is based on the Louvre cartoon after its cutting down not on the Ashmolean one.
7) The crown and martyr's palm indicate that someone has used the Louvre cartoon to transform it into an image of Sta Barbara (as in Palma Vecchio's painting), or possibly of Santa Caterina.
Connoisseurship is not needed in this case. The documentation and evidence of the surviving drawings exclude the possibility that the painting can be by Leonardo.