His years of teaching in Argentina and his first manifestos of "Spatialism".
Truly settled in Argentina, Fontana set to working as a sculptor, very avidly as always, and his work was met with great interest. His pieces were displayed at numerous exhibitions, and he received various awards. He was also appointed Professor of "Sculpting" at the Esquela de Artes Plasticas in Rosario, and at the same time he also taught "decoration" at the "Prilidiano Pueyrredòn" Academy of Fine Arts in Buenos Aires. In 1946, with Jorge Rornero Brest and Jorge Larco, he organized courses at the "Altamira, Escuela libre de artes plàsticas" in Buenos Aires, which became an important centre for cultural activities. From his contact with younger artists and intellectuals, and from the new ideas in research that he encountered, the Manifiesto Blanco was published in November in pamphlet form, compiled by Bernardo Arias, Horacio Cazenueve, and Marcos Fridman, and also signed by Pablo Arias, Rodolfo Burgos, Enrique Benito, César Bernal, Luis Coli, Alfredo Hansen and Jorge (Amelio) Rocamonte (Fontana did not sign the manifesto, probably because of his position, which was also officially recognized).
In the same year, the term "Concetto Spaziale" (Spatial Concept) appeared for the first time in the titles of a group of drawings by the artist, a term that was to accompany a large part of his output after this date. On 22nd March 1947 he again set off for Italy, on board the Vapore Argentina ship from Buenos Aires. Settling once more in Milano, he returned to Albissola to begin working again in ceramics, attracting a good amount of critical interest. In Milan, however, he came into contact with a group of young artists, and after meetings and debates, the first Manifesto dello Spazialismo (Manifesto of Spatialism) came into being in December, signed not only by Fontana, but also by the critic Giorgio Kaisserlian, the philosopher Beniamino Joppolo and the writer Milena Milani.
In 1948, the second drafting of the Manifesto (quickly followed by a third version: Proposta per un regolamento (Proposal for Regulations), 1950 reiterated the need to go beyond the art of the past, allowing "the picture to come out of its frame, the sculpture out of its glass case", and to produce new forms of art using the innovative means made available by technological progress.
Spurred on by the modernist momentum, in 1949 Fontana created an emblematic work at the Naviglio gallery in Milan: the Ambiente spaziale a luce nera (Spatial Environment in Black Light), in which a series of swaying phosphorescent elements hang from the ceiling in a completely black exhibition space. In the same year, he developed his research into spatial ideas with the start of his cycle of "Buchi" (Holes), pictorial works where the use of colours is joined by "whirls" of holes made with an awl.
His work as a ceramic sculpture continued, being celebrated in the exhibition Twentieth-Century Italian Art, at the MoMA in New York (1949), as well as in his one-man exhibition in May 1950 held at the 25th Venice Biennial. The year came to a close with his entry in the competition for the fifth set of doors to Milan Cathedral, organized by the Cathedral construction department.