Why are critics calling the Leonardo painting fake?

EVEN before Leonardo Da Vinci's Salvator Mundi went to auction last night at Christie's in New York, naysayers from around the art world were savaging its authenticity. Various advisers were muttering darkly, both online and in the auction previews, and one day before the sale New York magazine's Jerry Saltz wrote that though he's "no art historian or any kind of expert in old masters," just "one look at this painting tells me it's no Leonardo" .

And that was before the painting obliterated every previous auction record, selling, with premium, for US$450 million. Shortly after the gavel came down on Wednesday evening, the New York Times published a piece by the critic Jason Farago where, after also noting that he's "not the man to affirm or reject its attribution", declared that the painting is "a proficient but not especially distinguished religious picture from turn-of-the-16th-century Lombardy, put through a wringer of restorations."

Had the buyer of the most expensive painting in the world just purchased a piece of junk?