When Six and I met again in October, he was in a defiant mood. He has long dark hair that, when he is exasperated, tends to fall across his face like a curtain. He raked it back in place with one hand as he made his case. He insisted that Sander Bijl was just trying to cash in on Six’s own success. “When Dan Brown wrote ‘The Da Vinci Code,’ he had all kinds of lawsuits,” he said. “Frankly, I think I’m lucky I only have one guy coming after me.” He waved away my suggestion that his fixation on Rembrandt had clouded his professional judgment. He wouldn’t even credit the seemingly straightforward evidence that Bijl had spotted the portrait as a likely Rembrandt on his own. And he expressed bitterness that a plot by others, motivated, he said, by jealousy and greed, had marred what was to be his personal and professional breakthrough and obscured an unprecedented achievement: “In the history of mankind, nobody before has ever discovered two Rembrandts.”

Despite its decline in the market and in university syllabuses, Dutch old-masters art continues to have great popular appeal. The success over the years of the book and film “Girl With a Pearl Earring” and Donna Tartt’s novel “The Goldfinch” — which has a painting by the 17th-century Dutch artist Carel Fabritius at its center and is now being made into a movie — are mirrored in visitor attendance at museum exhibitions. Since the Rijksmuseum and the Mauritshuis reopened after renovations a few years ago, each institution has seen visitor numbers roughly double. “Within old masters, I think Dutch art is so much more approachable than, say, Italian religious art or overblown Baroque,” said Ronni Baer, curator at the Museum of Fine Arts, by way of explaining its popularity. “Everyone can understand a still life or an interior.”

If some in the Dutch old-masters world, who know how popular the art is among ordinary people and are hoping to reverse its decline in academia and the marketplace, cheered on Jan Six when he made his discoveries, it was surely because they saw him as an appealing young champion of the cause. He has the pedigree, of course. But beyond that, he so thoroughly grasps what makes this art special. By turning away from strictly religious subjects and highlighting the world around them — still lives, landscapes, pictures of one another — the painters of the time created works of art that are windows into who we are. People who devote their lives to the field do so out of a sense of dedication and treat it like a cause. “We have to fight for the importance of Dutch art,” said Emilie Gordenker, director of the Mauritshuis, the home of both Vermeer’s “Girl With a Pearl Earring” and Fabritius’s “The Goldfinch.” “We have to make sure the stories of these paintings still matter.”

Some of the top people in the field — museum directors, curators, academics — expressed disappointment in Six after his debacle, though none wanted to go on the record discussing it. “This is a very sad thing, because people already suspect art dealers of being slippery,” one said. “I can tell you some people are talking about Jan Six like Icarus.”

One dealer said that Six had made a young man’s mistake in dealing with the controversy: “He should have acted immediately to settle the matter quietly.” Even if he felt he was in the right, the dealer suggested, the prudent move would have been to reach a settlement in the name of preserving your reputation. “This business is entirely based on trust,” the dealer went on. “People have to trust you — and your painting.” To underscore the point, the dealer told me that he himself had asked a prominent buyer whether the buyer wanted him to get a price on one of the two paintings Six had unearthed, but that the buyer had responded, “Not with that controversy around it.”

In the broader world, though, controversies fade. The last time I spoke with Jan Six, in February, he was in an altogether different mood. To commemorate the 350th anniversary of Rembrandt’s death this year, the Dutch broadcaster NPO asked him to record a five-part TV series in which Six wanders through streets where the painter lived, stops in front of the building in Leiden where he went to school and muses before various masterpieces. It’s Six doing what he does best: communicating his passion, this time to a very broad audience, which is new for him. “There are hundreds of thousands of people watching me on the telly and enjoying it,” he said. “Suddenly all kinds of people are contacting me. Some have an old painting they want me to look at. A woman just called me. She said she’s turning 75, and her twin sister is crazy about Rembrandt. She asked if there was some way I would stop in at their birthday lunch and talk about Rembrandt for 10 minutes. So sweet — of course I’ll go! This has given me a great boost.”

It has also given him some distance from “the bubble,” as he referred to the art elite, and allowed him to begin to move on from his thrilling and excruciating year. “It was epic and fantastic,” he said, “and then everything changed. I realized that being so obsessed with a painter is not necessarily a good thing. But of course I still am.”