James Beck, Professor of Art History at Columbia University, New York, was, to use one of his own favourite technical phrases, an unicum, a “one-off” – a scholar who married an impeccable professional method with respect for artists, their views and their historical legacies.

To the discomfiture of some art historical colleagues, he saw artists as allies. His declared solidarity with artist-critics of restorations was to carry him beyond the boundaries of academia into increasingly bruising art-political engagements.

Born in New Rochelle, New York, in 1930, Beck graduated in history and political science in 1952 at Oberlin College, where he had also studied painting. Aspiring to become a professional painter, he took a master’s degree in studio art at New York University in 1954 before moving to Florence for further painting studies at the Accademia delle Belle Arti.

In Florence he met his future wife and lifelong partner, Darma, and fell under the sway of Italian Renaissance art. After teaching art and art history at the universities of Alabama and Arizona State, he took a PhD in art history at Columbia University in 1963 under the tutelage of the great German scholar Rudolf Wittkower and the influence of Charles de Tolnay, the legendary specialist in Michelangelo.

For nearly two and a half untroubled decades Beck alternated between New York and his beloved adoptive Italy. He produced many books and scholarly articles on sculptors such as Donatello, Ghiberti, Brunelleschi, Michelozzo, Pietro Lombardo, Antonio Rossellino, Niccolò dell’Arca and, above all, Jacopo della Quercia and Michelangelo. His dedication to these last two was to cost him dear.

In 1986, joining forces with artist-critics of the cleaning of Michelangelo’s Sistine Chapel ceiling frescoes, he incurred the wrath of the art-historical establishment, some of whose leading members had been, Beck felt, lazily complacent about an experimental restoration project that was proving as radically controversial aesthetically as it was methodologically untested.

Beck’s opposition to the restoration, which was funded by Nippon Television Corporation to the tune of $3 million, caused him to suffer vicious professional abuse and even social ostracism within liberal New York’s art-world high society – notwithstanding the acclaimed and exemplary scholarship in his book Doors of the Florentine Baptistery and the perennial appeal of his classic, comprehensive survey Italian Renaissance Painting.

The “battle of the Sistina” was followed almost immediately by a second, more personally threatening furore, concerning Beck’s “own” Renaissance sculptor, the subject of his doctorate, Jacopo della Quercia.

Beck’s publications on the artist began in 1962 with his earliest article (“An Important New Document for Jacopo della Quercia in Bologna”), included a beautifully illustrated book in 1988-89 on the marble tomb of Ilaria del Carretto, and ended in 1991 with a magisterial two-volume, standard monograph on Della Quercia, which assembled 506 documents pertaining to the artist.

As these lifelong studies were reaching final formulation, the Ilaria tomb (regarded by Ruskin and Beck alike as the most beautiful effigy of a woman in Italy) underwent a disastrous restoration, during which it was stripped of its ancient mellow patina (by chemical poultices and abrasion with air-borne particulates) and then “reglossed” with a penetrating, oil-based coating. Beck’s condemnation of the restoration, in the presence of the tomb in Lucca Cathedral in July 1990, was reported in four Italian newspapers.

Those reports triggered four separate actions for criminal libel by the restorer against Beck. The charges carried a possible prison sentence of three years (and ruinous civil damages).

Against the advice of his closest colleagues and one of his own lawyers, Beck resolved on a point of principle to defend his right, as the world’s leading authority on Quercia, to speak for the preservation of the artist’s work. Not a single scholar defended Beck in public in the run-up to the trial because it was widely believed that he would lose. That was also the view of the trial judge in Florence who was overheard (by an intern-lawyer and former policeman working for Beck’s lawyers) confiding to the prosecuting lawyer as they left the court together at the end of the first session: “. . . eh, but I shall convict him”. In the event, after an unsuccessful attempt to have the judge replaced, Beck was acquitted.

The terrifying ordeal of the trial had a chain of consequences. First, it caused Beck to recognise the need for an organisation dedicated to defending both the interests and the integrity of art objects and the right of scholars freely to discuss treatments imposed upon them at the hands of technicians abetted by corporate sponsors. As a result, he founded the monitoring and campaigning organisation, ArtWatch International, in 1992.

Beck collaborated with his long-term ally, the British artist (and present director of ArtWatch UK) Michael Daley, to produce Art Restoration – The Culture, the Business, the Scandal (1993), a book which anatomised controversial restorations in Italy and at the National Gallery in London.

In November 1993, in a review for The New York Review of Books, Charles Hope, the Renaissance scholar (and the present director of the Warburg Institute), wrote that having been, like many other art historians, initially enthusiastic about the Sistine Chapel restoration, he now recognised that “my earlier enthusiasm had been misplaced” and that Beck had “in the face of hostility from his professional colleagues and even a threat to his liberty, done a valuable service to everyone who cares about the art of the past”.

Beck’s impassioned pursuit of scholarly researches and public campaigning continued unabated until his recent illness. His newly published book, From Duccio to Raphael – Connoisseurship in Crisis, a critique of the processes by which secondary paintings get upgraded on questionable methodological practices to Old Master status, may prove to be his most explosive yet, if his final call for a more effective legal oversight of the art market be heeded.

Certainly, the detailed, scrupulously painstaking case he establishes for such supervision constitutes, for the established art scholarly/market nexus, a call to account. It begins: “Two paintings, a mini aspiring Raphael da Urbino Madonna and an equally tiny aspiring Duccio di Buoninsegna Madonna were sold for record prices in 2004. The first was bought by London’s National Gallery and the second by New York’s Metropolitan Museum of Art. These objects and the mode in which the attributions to their famous presumed authors were achieved, document a breakdown in modern connoisseurship . . . In addition to what is regarded as a monumental failure on the part of experts, the use and misuse of public funds is an issue that lies just beneath the surface.”

Beck’s scholarship and probity earned many honours and awards throughout his long career – his favourite being the title Commendatore di Merito della Repubblica Italiana bestowed in 1992.

These honours notwithstanding, he remained a most affably approachable teacher and colleague. In the introduction to Watching Art: Writings in Honor of James Beck (published in 2006 on his 76th birthday), two former students, Mark Zucker and Lynn Catterson, in testifying to his being “a great teacher”, conjure the delightful and productive bustle of his office: “He is there everyday, usually in the company of two or three students discussing their projects and, it seems, almost threatening to crowd him out of his own workspace. . . students may not even be aware of the exquisite attention he pays to the details of their conversations.”

One source of Beck’s strengths was a remarkable dynamic physical energy – until late in life he played basketball every weekend with students and colleagues, some less than half his age.

James Beck is survived by his wife, Darma, his daughter and son.

Professor James Beck, art historian, was born on May 14, 1930. He died of lung cancer on May 26, 2007, aged 77