Hultberg’s work with large-scale enamel murals continued in the late 1950s and in 1956, Hultberg and his wife Ethel moved with their four children to the Gate Hill Cooperative, the renowned artist coop in Rockland County, New York. Close friends with artist John Cage, the Hultbergs were amongst the minority in the coop that had not been part of the famed Black Mountain College Community yet still forged deep bonds with the artistic community and collaborated with many of the residents. During this time Hultberg’s work continued to gain national recognition. In particular, one work, Burnt Sun, a large-scale multi panel work exhibited at Syracuse Ceramic National, cemented him as a pioneer alongside expressionists such as Jackson Pollock.

For the next two decades, Hultberg continued to be an enduring presence in the abstract expressionist movement with his work featuring in the 1962 Seattle World’s Fair, and in the Pavilion of American Interiors at the 1964 New York World’s Fair. In 1966, while represented by Lee Nordness Gallery, Hultberg presented a solo show at the Museum of Contemporary Crafts in NYC and in 1969 his work was included in the seminal exhibition Objects: USA. During these years Hultberg also continued to undertake large scale commissions including enameling the side of a 4-story escalator for the Busch Gardens complex in Tampa, Florida - at the time the longest continuous motor stairway ever built. He was also commissioned to produce a pair of large enameled doors for the Living Theater in NYC and an impressive 45-foot Mural on Aluminum for Alcoa Corporation, Pan Am Building, NYC.

In the mid-1970s, Hultberg took a hiatus from enameling to focus on expressionist portraiture in acrylic on canvas before being sought out in the 1980s to produce a series of sixteen 4ft. x 5ft. enameled panels entitled Apple Dapple commissioned for the Metromedia building lobby in Manhattan. In later life, he and his wife Ethel retired to the South of France where Hultberg passed away in 2019.