[6] He supported his studies with work at the prestigious commercial art gallery of Giuseppe Sangiorgi which filled a large part of the vast interior at the Palazzo Borghese.
[2] Here he "undertook the duties of an apprentice decorator and copyist of classic works under the guidance of Maestro Oreste Morozzi" (who appears to have combined the roles of head gardener and chief curator at the palace).
[6] In 1907 he started attending the academy's "Scuola libera del nudo" ("Free School of The Nude") in the Villa Medici, as a result of which he became more closely acquainted with Umberto Boccioni and Mario Sironi.
[3][9] He embarked on a more public career in 1910/1911 as a caricaturist for the newly launched "Idea Nazionale", a political Rome-based newspaper published weekly between 1911 and 1914, supportive of the anti-Austrian Italian Nationalist Association.
The display included his "Castello del Mistero",[14] a dark and shadowy work believed to have been powerfully influenced by symbolism and neo-Impressionist divisionism.
[12] Emilio Cecchi, another highly respected art critic who was in addition a close friend, describes Òppo's pictures from this time as employing "colours of an acrid, biting, almost burning" character, reflecting little of the Italian modernism of artistic contemporaries, but rather imbued with "a certain Matissian influence".
[6][15][16] The critic Alberto Cantù, writing in 1914, was struck by the "violence, aggression and capacity for all excesses before finding its equilibrium" apparent in Òppo's paintings.
[6][18] The journal "Idea Nazionale", to which Òppo contributed, was transformed from a weekly publication to a daily one in 1914, primarily in order to campaign for the Italian government to intervene militarily in the war which had broken out north of the Alps.
During the 1930s and 1940s, he believed he should abstain from exhibiting in Italy, precisely because of his political-administrative activity in the artistic field, not that this stopped his participating in several shows abroad, such as L'art italien des XIX et XX siècles (19th and 20th Century Italian Art) at the Jeu de Paume in Paris in 1935 and at the 1939 New York World's Fair.