Ostroukhov's study of a horse, taken for a Velázquez, proved to be by Van Dyck
Ilya Ostroukhov, former director of the Tretyakov Gallery, acquired in the 1920s an unusual study of a bored horse for his collection, having swapped it for a study of Menippus. Ostroukhov was immensely proud of his purchase, believing he had secured so original a Velázquez for his private collection, until the drawing caught the eye of the eminent Moscow art historian Ekaterina Goldinger, who at once denied that the work was by Velázquez's hand.
Ostroukhov then conjectured that the study had been painted by Théodore Géricault, but this version, too, failed to satisfy Ekaterina Vasilyevna, a lady noted for her peremptoriness and her attention to detail. The collector even requested a photograph of the authentic Géricault in the museum at Grenoble in order to prove the worth of his acquisition. Soon, however, he was himself obliged to admit that the horse was not by Géricault.
The obstinate Goldinger eventually demonstrated that the drawing had been executed by none other than Van Dyck. Such was the unexpected outcome of an exchange.