Well what can I say. This is a very odd book. In fact it is really two books in one. But that is not necessarily a good thing.
On the one hand we have a fictional story that is not very well written at all, in fact it is for the most part dire. I don't want to give too much away but I am never convinced by any story that includes the thoughts of a dog as part of the narrative. The time travel part is also handled appallingly.
So a fail on the fiction side of things.
The actual information about the painting, and it is one of the most wonderful paintings ever to have been painted, is at times utterly fascinating. Lots of useful insights and interpretations as well as what is available from historical fact.
However, whilst the author clearly knows his stuff in regard to the painting the fiction is dreadful. This would have made a great art history book if it had just focused on the painting and left out the fiction.
Have always been interested in this painting and so the book of special interest to me, but it would be an enjoyable read whether you have ever seen the painting or not.