The concept of inganno dell’occhio strongly influenced the Venetian monumental painting of the 18th century. In the works jointly executed by Gerolamo Mengozzi Colonna and Giambattista Tiepolo, illusionism reached its highpoint. Yet there are different genres and degrees of illusionism. This article examines conscious visual interruptions as reflections of a multi-faceted context. This includes a newly awakened interest in optics, in particular in the theories of Isaac Newton. Consequently, fascination with the operating principle of the eye and reflections on the visual process are central themes, for instance, also in Francesco Algarotti’s Newtonianismo per le Dame, and give meraviglia – which should capture the attention of the beholder – a new quality. New media such as the laterna magica and peep-boxes influenced viewing habits and had an impact on the evaluation of painting. In the ballroom of Palazzo Labia, the viewer’s imagination is stimulated by the fragmented portrayal of individual motifs. At the same time, the choice of illustrated instances of illusionism increased, as dramatic moments of action were intentionally omitted. Nevertheless, allegories and themes drawn from ancient history and mythology became the object of criticism. The revaluation of bearing visual witness and the criticism of rhetorical concepts led people to question the value of allegorical pictorial programmes and increased the appreciation of genre scenes. The mural paintings in the Valmarana villa and foresteria show a wide range of forms of illusionism and work purposefully with visual interruptions, which reveal the illusionism and confront the viewer with the relativity of his sight. In several of Giandomenico Tiepolo’s works, such as, for example, Mondo Nuovo, the act of seeing, or rather the pleasure of viewing, becomes the actual theme of the painting combined with a criticism of the new medium.