The most majestic holy painting by Diotti is The beheading of St John the Baptist (1825), of which the Diotti Museum exhibits a preparatory draw related to the Baptist's figure and this oil sketch.
The painting was exhibited in Brera and then collocated in the Church of Stezzano (Bergamo). It was celebrated from the press of that period and shows how Diotti loved to conciliate his basic neoclassicism with sixteenth-century enlightenment reminiscence and seventeenth-century realism, favouring those "night light" effects, which had already characterized the roman pensioner in Adoration of the shepherds and will reappear in the later Kiss of Judas and in the Petrobelli Altarpiece.
The collocation of the painting in the Church of Stezzano was very problematic and that caused in Diotti a sense of disappointment. The elaboration of the piece took three years (1817-1820) and, at the moment of delivery, Diotti found the location behind the altar lightly distorted (two apsis windows were shaded during renovations), making the canvas invisible.
A chapel in the nave was demolished only in 1843/44, to allow the painting a more respectable position, and another bigger chapel was built in neoclassical style, which could include the great altarpiece. Some frescos for the walls of the apsis were commissioned to Enrico Scuri, who was Diotti's student, and he will be destined to succeed him in the supervision of the Accademia Carrara.
