Long attributed to Lorenze di Credi, new research suggesting a small panel painting at the Worcester Art Museum is actually by one of the greatest masters of the Italian Renaissance.

For decades, a small Italian Renaissance painting owned by the Worcester Art Museum (WAM) was attributed to the Florentine artist Lorenzo di Credi. Now, after careful study of it that spanned 20 years, “A Miracle of Saint Donatus of Arezzo” has returned to public eye, and it bears new and astonishing authorship. Its label still carries di Credi’s name, but the true artist responsible, conservators believe, was actually Leonardo da Vinci. Just 23-years-old at the time, Leonardo would have painted it as a young student in the workshop of Andrea del Verrocchio, where di Credi, another student, likely played an incidental role in its creation.

This newly attributed Leonardo is the centerpiece of an ongoing exhibition at WAM that explores its mysterious origins and history. The painting, which depicts the Bishop Saint Donato helping a tax collector find his money, was originally part of a predella from an altarpiece that still decorates the Duomo di Pistoia. Like countless other Italian Renaissance painted panels, this wooden base was cut up, and its three fragments were sold, likely in the Napoleonic era. One is lost, while another was acquired by the Louvre in 1863. Depicting the scene of the annunciation, this panel is on loan to WAM for its exhibition, uniting the two fragments for the first time since their separation.

Commissioned in 1475 from Verrocchio’s studio, the predella was known to have been painted by multiple hands, but exactly who contributed, and to what extent, has long been debated. In fact, WAM’s panel, was actually attributed to Leonardo when it surfaced in 1933 at an art sale, where patrons of WAM purchased it. But when the panel was exhibited that year at the Century of Progress, Chicago’s World’s Fair, its authorship immediately drew suspicion. Art historians wrote to the museum, expressing their various opinions on whether or not it was a genuine Leonardo.

It wasn’t until the 1970s that Lorenzo received full credit for the painting. The museum wanted to publish a catalogue of its European paintings, and invited the late Martin Davies, director of London’s National Gallery, to write entries.

“Davies downgraded it to Lorenzo di Credi,” Rita Albertson, WAM’s chief conservator, told Hyperallergic. His decision essentially erased Leonardo from the picture for the next two decades. “Although Lorenzo di Credi is a charming artist he’s not the most important artist of the time. People really stopped coming to look at the painting before they would publish, repeating what had been written before.”

One curator who did visit the painting, in 1995, was Laurence Kanter, now Yale University Art Gallery’s chief curator. Then a curator at the Metropolitan Museum of Art, Kanter questioned the authorship printed on the wall text. He asked WAM’s director to reexamine the painting, pointing out the exceptional detail of Donatus’s blue robe.

“He was looking for brilliance, and he saw the hand of Leonardo, particularly in the robe,” Albertson said. “To his eye, it was clear that Lorenzo di Credi never reached that level of competency.”

Kanter’s questions were strong enough reason for the museum to move the painting to its conservation department for study, where it has resided for the last two decades. In that time, WAM has used x-radiography, infrared reflectography, and x-ray fluorescence to closely examine it. It compared this information with corresponding data observed from the Louvre’s panel, which was always identified as a work by Leonardo, with possible touches by Lorenzo. They found that the landscapes in both are nearly identically in conception and execution.

Advances in technology have also allowed this generation of curators to examine the painting’s underdrawings as never before. Much of it appears sketchy, but preliminary architectural drawings were later reinforced with a ruler, suggesting that someone with a strong interest in perspective — like Leonardo — took extra steps to convey accuracy. The drawing of the bishop also carries a particular delicacy that suggests careful thinking of the body’s underlying structure — how it moves and carries weight.

“Leonardo is interested in the character of the person,” Albertson said. “He’s paying attention to the wrinkles of the face, the reflection in the eyeballs. You see a person who has compassion and an expression of serenity, opposed to Lorenzo’s figures, which really represent the idea of a person.”

The exhibition also features a painting by Lorenzo, “The Annunciation” (c. 1475-1478), for comparison. The scene is more linear and schematic, and it shows the artist’s use of local color. Curators believe that Lorenzo painted the red robe of the tax collector in “A Miracle of Saint Donatus of Arezzo,” but the tonality of the blue in the Donatus’s robe, which has a shimmering iridescence, suggests that Leonardo painted these details. Notably, both predella panels show experimental uses of oil paint, which Leonardo used to create expressive detail; Lorenzo, in comparison, was trained in egg tempera — the predominant method used in Renaissance painting.

“We could very clearly see that [WAM’s painting] was worked on over a period of time by several different hands, by people with different mentalities and skills,” Albertson said. “The more we’ve studied Verrocchio, we come to understand that he relied on collaboration in just about every painting from his workshop. It was a business; they were just trying to get the work done.”

In the last few years, Alberton has studied many di Credi paintings and invited curators of Italian art to look at the predella fragment through a microscope. She has heard a range of expert opinions, and acknowledges that the new attribution will draw controversy.

“It took me a long time to be convinced,” she said. “Whenever you’re dealing with Leonardo it’s always going to be controversial as people bring their own experiences and prejudices.

“This is mostly an invitation for people to look closely and try to make connections about Leonardo as a student. We know his mature work, which is off-the-charts incredible. But this, to us, is where he began. This is the beginning of Leonardo as a painter.”

After WAM’s exhibition, the painting will travel to Yale University Art Gallery, then to Florence, where it will be part of a show on Verrocchio. The Louvre, too, has requested it, for inclusion in its blockbuster Leonardo exhibition, set to open next year to mark the 500th anniversary of the artist’s death.

The Mystery of Worcester’s Leonardo continues at the Worcester Art Museum (55 Salisbury St, Worcester, MA) through June 3.