Although Gustav Gaul is not mentioned in Wagner’s correspondence or autobiography, he was clearly a part of the social circle that Wagner engaged with when he visited Vienna in the early 1860s and in 1875.
Gaul made a number of sketches of the composer, including three recently found in the Nachlaβ of his papers at the Österreichische Nationalbibliothek (A-Wn Autogr. 194/3-1, 3-2, and 3-4); two are from a meeting of October 1861 at the Hotel Kaiserin Elisabeth (above and inset), one of them depicting Peter Cornelius, Karl Tausig, and Gaul himself (far right), as well as Wagner wearing a pince-nez.
This according to “Richard Wagner and the artist Gustav Gaul: Newly discovered drawings in the Austrian National Library” by Chris Walton (The Wagner journal XV/1  43–49; RILM Abstracts of Music Literature 2021-1807).
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