His Neon for the Triennial, his research in the fifties, and his short cycles "Quanta" and "Nature".
Judging for the designs for the Milan Cathedral doors took place on 25th April 1951. Together with Luciano Minguzzi, Francesco Messina and Enrico Manfrini, Fontana was entered into the final part of the competition (he was joint winner in 1952 with Minguzzi) and his creations were displayed in the central hall of the 9th Triennial in Milano. He also created a vast neon arabesque for the Triennial above the grand staircase, and a ceiling of indirect light in the vestibule and the hall, both part of an environmental structure designed by the architects Luciano Baldessarri and Marcello Grisotti.
In addition, on the 26th November he signed the fourth Manifesto of Spatial Art with Anton Giulio Ambrosini, Giancarlo Carozzi, Roberto Crippa, Mario De Luigi, Gianni Dova, Virgilio Guidi, Beniamino Joppolo, Milena Milani, Berto Morucchio, Cesare Peverelli and Vinicio Vianello. He continued to work assiduously on his cycle of "Holes", lending these works for the first time to the 1952 Spatial Art exhibition at the Naviglio gallery in Milan. In the same year in Milan, he married Teresita Rasini, who he had met in 1930, and he transferred his Milan studio from Via Prina no. 23 to Corso Monforte, his final address.
On the 17th May he signed the Manifesto del movimento spaziale per la televisione (Manifesto of the Spatial Movement for Television) with Anton Giulio Ambrosini, Alberto Burri, Roberto Crippa, Mario De Luigi, Bruno De Toffoli, Gianni Dova, Enrico Donati, Giancarlo Carozzi, Virgilio Guidi, Beniamino Joppolo, Guido La Regina, Milena Milani, Berto Morucchio, Cesare Peverelli, Tancredi and Vinicio Vianello, and with some of his works he took part in experimental broadcasts from the RAI television studios in Milan. In the fifties, Fontana took part in numerous important international exhibitions, and he continued unremittingly with his research in the field of painting. In addition to his "Holes" motif, his canvases began to be enriched with dense elements of colour, and with fragments of glass, giving rise to his cycle of works known as "Pietre" ("Stones"), hailed by the critics in 1955 when they were displayed at the 7th Rome Quadrennial. From 1954 he began developing his style further, accompanying his cycle of "Stones" with new creations, identified as his series of "Gessi" ("Impastos", 1954-1958) and his series of "Barocchi" ("Baroques", 1954-1957). At the 29th Venice Biennial (1958), he was given an entire room to display his most recent works. Alongside his "Impastos" and his "Baroques", he also showed some of his "Inchiostri" ("Inks") and his spatial sculptures on rods, that the artist had begun working on from 1957. At the peak of his research in this decade, the "Tagli" ("Slashes") series took shape, conceived at the end of 1958 and presented at his one-man show at the Naviglio gallery in February 1959 and shortly after at the Stadler gallery in Paris (March 1959), then at Documenta in Kassel (July 1959), at the 5th San Paolo Biennial in Brazil (September 1959), at the critical retrospective exhibition organized by Crispolti at the L'Attico gallery in Rome (October 1959), at the Schmela gallery in Dusseldorf (1960), and lastly at his one-man show at McRoberts & Tunnard in London (1960).
During this very invigorating period for the artist, two other short series also emerged. His series of "Quanta" (1958-1960) is a group of polygonal canvases with slashes, arranged in different patterns, while his "Nature" ("Nature Sculptures" 1959 and 1960) series includes clay and bronze works conceived at Albissola.