THE New Generation sculptors burst on to the London scene in 1965 to critical acclaim and public bewilderment. Their colourful abstract forms, distant from the tradition of European figurative sculpture and inspired by a dynamic Modernist aesthetic from America, changed British sculpture.

For the sculptors in the Whitechapel Gallery’s ground-breaking show, it was a defining moment. For Isaac Witkin it launched an international career. Enrolled in the sculpture department of St Martin’s School of Art in 1957, he was at the centre of innovation. The department, under Frank Martin and Anthony Caro, and with students such as Phillip King, William Tucker, David Annesley and Michael Bolus, was about to enter its heyday.

Supported by the critic Clement Greenberg, these artists challenged assumptions about sculpture and its functions. Greenberg declared: “St Martin’s should be one of the prides of England. Some of its graduates are producing the most distinctive and strongest new sculpture done anywhere in the world at this moment.”

Ahistorical, pristine and above all abstract, the work consisted of outlandish shapes fabricated in such unfamiliar materials as fibreglass and painted in vibrant colours.

Witkin, who was born in Johannesburg in 1936, recalled his time at St Martin’s as one of exhilaration and inspiration: “Students were changing the face of international art,” he said. “An artistic revolution was happening in the context of an art school.” He graduated in 1960 and in 1961 started as an apprentice to Henry Moore.

He acknowledged his debt to the master: “Moore changed my understanding of organic form in a very basic way that serves me to this day. Working for Moore was extraordinary. He made me realise how little I really knew about sculpture. He turned out to be the missing link in my education.”

Witkin refused to sign a letter to The Times on May 26, 1968, in which 41 artists, including Caro, King, Elizabeth Frink, Howard Hodgkin and Eduardo Paolozzi, deplored a proposal that the Tate purchase two dozen of Moore’s works for £400,000.

Witkin left Moore in 1963 and in the same year had his first solo exhibition at the Rowan Gallery, in which he revealed himself to be an accomplished craftsman whose self-contained, sensitive personality informed his work.

Bryan Robertson, the director of the Whitechapel Gallery, distinguished Witkin from his peers: “He, more than the others, translated the underlying aims of traditional sculpture into a more modern sculptural language.”

For two years Witkin taught in the sculpture department of St Martin’s. Like other sculptors of his generation, including Caro and King, he then moved to the US, to be artist in residence at Bennington College, Vermont. Bennington was home to a community of artists dubbed “the Green Mountain boys”. Many taught in the college’s art department and others, such as the painter Kenneth Noland, lived close by. Greenberg was a regular visitor, as were Helen Frankenthaler, Larry Poons, Paul Feeley and Jules Olitski.

Sadly for Witkin, the sculptor he most admired, David Smith, died in a car accident a week before his arrival. Witkin visited Smith’s studio, and this experience reinforced his commitment to formalist abstract sculpture, as seen in the welded steel works that he produced at Bennington. His heavy industrial steel forms with complex Cubist compositions also recall the innovations by Caro.

Witkin was included in the Primary Structures show at the Jewish Museum, New York, in 1966, the first big exhibition devoted to Minimalism. It was a propitious start to his US career and confirmed his reputation as a leading formalist sculptor. Throughout the 1970s he regularly exhibited his welded-steel sculptures in New York. He became a US citizen in 1975.

In 1978 he was introduced to New Jersey as an artist in residence at the Johnson Atelier, a new foundry in Princeton. Free to experiment, he learnt the range of sculptural processes, from hollow casting to direct pouring, and he cited the experience as the beginning of his breakthrough as an artist.

He also evolved his signature abstract sand-cast sculptures after seeing casting spills in foundries. Done by creating shapes in wet sand and then splashing molten metal into the forms, this unusual technique gave rise to biomorphic shapes, unlike his hard-edged steel forms, which he assembled into monumental compositions.

From the late 1970s he worked mainly in bronze: “I develop my process of creating language out of the behavioural flow of metal, wresting order from chaos,” he said. Rather than applying paint, he used chemicals to create rich patinas ranging from green to yellow to brown.

In 1987 Witkin bought a small farm in Burlington County, to house his collection of African art. Nine large sculptures stood in the grounds of his property, providing a private survey of his career.

In the past 20 years he taught at the Parsons School of Design, New York, and Philadelphia College of Art.

He was also involved with the large Grounds for Sculpture Park in Hamilton Township, New Jersey. He persuaded the artist and patron J. Seward Johnson Jr, heir to the Johnson & Johnson fortune, to buy the property when it was the abandoned state fairground, and in 1996 he was the first artist to have a solo show in its grounds. Six of his sculptures are in its permanent collection.

His work is also held in museums the Smithsonian American Art Museum, Washington, and the Tate, London.

Isaac Witkin was divorced from Thelma Appel, whom he married in 1961. He is survived by his two daughters.

Isaac Witkin, sculptor, was born on May 10, 1936. He died on April 23, 2006, aged 69.