Art authentication can be a tricky business. Seasoned experts can be fooled by forgeries or miss important clues that could cement the authorship of a particular piece. At stake: reputations of museums and millions of dollars.

The art world’s latest controversy arrived Tuesday, when two prominent scholars of Post-Impressionist artist Vincent van Gogh declared that a 65-page sketchbook passed down as a family heirloom in France was once owned by the uni-eared painter.

Amsterdam’s Van Gogh Museum, however, fired back with an open letter claiming the sketchbook was not the genuine article. Using their library of more than 500 van Gogh drawings as a reference, museum staffers wrote that the illustrations aren’t indicative of the artist’s development circa 1888 and that the brown ink used was inconsistent with his preference of black or purple ink.

It’s believed that van Gogh gifted the proprietors of a hotel in Arles, France with the sketchbook after he had been remanded to a mental institution after slicing off his ear; van Gogh had asked his doctor, Felix Rey, to pass it along to the Ginouxs, who welcomed the artist as their guest and had given him a ledger in which to draw. The museum argues that Rey had left Arles by then and had never come to visit him.

One of the scholars endorsing the work as genuine, Bogomila Welsh-Ovcharov, is a highly-respected van Gogh expert who has just issued a book titled Vincent van Gogh: The Lost Arles Sketchbook, featuring commentary and reproductions of select illustrations. Welsh-Ovcharov spent three years researching the sketches after discovering them in 2013. The book, she said, was in the Ginoux family for decades before it came into the possession of a neighbor, who was unaware of its significance. The neighbor's daughter thought little of it until a friend suggested she show it to an art historian.

Welsh-Ovcharov maintains that an entry in the hotel’s 1890 date book supports her version of events. In it, an employee of the Ginouxs wrote: “Monsieur Doctor Rey left for M. and Mme. Ginoux from the painter Van Goghe [sic] some empty olive boxes and a bundle of checked towels as well as a large book of drawings and apologizes for the delay.”

[h/t The New York Times]