Michael Gallagher, the head of paintings conservation at the Metropolitan Museum of Art, looks at paintings all day long, so, understandably, light is important to him.

His usual work space, the 18,000-square-foot Sherman Fairchild Paintings Conservation Center, is filled with it.

But the center is currently undergoing a renovation, the first since it opened in 1980. Earlier this month, Mr. Gallagher and his staff of 10 moved to a space in the European paintings galleries, where, on a recent morning, Mr. Gallagher was still adjusting to the cramped space and the rainyday gloom.

Having to relocate was an inconvenience, but it also offered an opportunity. Since Mr. Gallagher arrived at the Met in 2005, Sir Joshua Reynolds’s massive group portrait “The Honorable Henry Fane (1739–1802) with his guardians Inigo Jones and Charles Blair” has been on his list of paintings to restore.

The problem was that, at 8 feet high and almost 12 feet long, the painting is too large to move. When Mr. Gallagher was looking for a temporary work space, he came up with a solution: Since he couldn’t bring the Reynolds to the conservation studio, he would bring the conservation studio to the Reynolds. So he brokered a deal with the European paintings department to take over this gallery for a year.

The Reynolds was acquired by the Met in 1887 and hasn’t been restored since the 1950s, when it was finished with a synthetic varnish that was popular back then but is no longer used. Though once believed to cause less discoloration than natural resin, the varnish has over time given the painting a plasticlike surface, Mr. Gallagher said, and an overall milky grayness that diminishes the colors and flattens the picture plane.

In a sense, the varnish just exacerbates problems that are endemic with Reynolds, who “experimented with really quite alarming combinations of media,” Mr. Gallagher said. Even in the 18th century, the tendency of Reynolds’s paintings to age badly was so notorious that one of his clients, Sir Walter Blackett, later complained in verse: “Painting of old was surely well designed / To keep the features of the dead in mind, / But this great rascal has reversed the plan, / And made his pictures die before the man.”

Fortunately, Reynolds painted the Henry Fane group early in his career, Mr. Gallagher said, “before he really went off the Richter scale.” Although the flesh tones have faded somewhat, the men’s faces are not the cadaverous gray of some of his subjects. “I’m encouraged that you still have rosy tones,” Mr. Gallagher said, pointing to Fane’s cheek.

In his two years at the Met, Mr. Gallagher — whose full title is the Sherman Fairchild Conservator in Charge of Paintings Conservation — has earned his colleagues’ respect. A curator of European painting, Keith Christiansen, said that besides trusting absolutely his instincts about conservation, he also values Mr. Gallagher’s taste. “If I went and saw something that I thought merited consideration for acquisition,” he said, “I would pay very careful attention to his aesthetic response, even if I knew more about the artist. His visual sensitivity is extremely acute.”

Mr. Gallagher didn’t decide to become a conservator until his mid-20s. He had a degree in studio art but didn’t know what he wanted to do. “I sort of knew on one level that I wasn’t really a painter,” he said. “I knew that I loved being around pictures, but conservation wasn’t on my radar.” Then he saw an exhibition of a group of bronzes that had undergone a 16-year restoration, and it set him thinking.

“Out of sheer ignorance I rang the National Gallery and said, ‘Could I speak to paintings conservation?’ and I asked, ‘How do you become a paintings conservator?'”

Miraculously, the person who answered the phone was patient enough to answer his question. “She said that science was important, but it wasn’t everything — you also needed interest in art history, manual dexterity, eye. And I became convinced it was the right thing for me.”

He attended the Hamilton Kerr Institute at the Fitzwilliam Museum at the University of Cambridge, a three-year program that at the time accepted only two students per year. “It was one of the happiest periods of my life,” he said of his training. “We spent an afternoon looking at this Frans Hals painting in infrared to examine the underdrawing, and I remember thinking, ‘I can’t believe I got a grant to do this!'”

He worked at the J. Paul Getty Museum, the Kimbell Art Museum, the Gemäldegalerie in Berlin, and the National Galleries of Scotland before being hired by the Met to replace the previous head of paintings conservation, Hubert von Sonnenburg, who had died. “It was like a dream,” he said of the Met job. “It’s been for years one of the really great departments.”

The Met’s conservation center, which opened in 1980, was built with a $1.5 million grant from the Sherman Fairchild Foundation. It is a wonderful space with huge windows, Mr. Gallagher said, housing studios, laboratories for the scientists, offices, a seminar room, and a library. But after almost 30 years, the space was showing its age. Most crucially, conservators’ increasing dependence on computers necessitates more office space. The renovation, for which the Sherman Fairchild Foundation has given over $6 million, will add 1,000 square feet and rearrange the office space. The glass on the roof will also be upgraded.

Restorations have often become the subject of controversy, particularly when they involve iconic works of art. The cleaning of the Sistine Chapel ceiling in the 1980s provoked intense debate, between those who wanted the frescoes to look as they’d always looked — august and old — and those who argued that the bright colors the cleaning uncovered were actually closer to Michelangelo’s intentions.

The approach of conservators themselves has changed over the years. “There was a strong move in the ’50s to be taken more seriously as a scientific profession,” Mr. Gallagher explained. Conservators then generally favored new synthetic varnishes over natural resins, which produce the toffee brown color of Old Master paintings. Today, conservators tend to take a case-by-case approach that is more sensitive to individual works.

While some basic techniques of conservation remain timeless — when a reporter visited the studio, a colleague of Mr. Gallagher’s was retouching another 18th-century portrait with a brush and little pots of paint — others are constantly being revised. Digital photography has changed things dramatically. Conservators now document their own projects with hundreds of photographs. The practice of infrared reflectography, which captures the underdrawing in a painting, is conducted with digital technology. “The materials and the techniques we use as conservators are continually being examined,” Mr. Gallagher said. New synthetic varnishes are invented and age-tested to determine their stability. Even simple tips, like a new way to fix keys into a stretcher, are passed along to colleagues.

Mr. Gallagher gave a talk earlier this year about the recently completed restoration of a work by the Italian Rococo painter Corrado Giaquinto. His approach to the job was characteristically minimalist. The painting, unusually for a picture of that age, was unlined, and partly as a result was in excellent condition, although there was some “cupping” — places where the paint layer has developed dishlike formations. Mr. Gallagher made some efforts to reduce the cupping locally, but the only full solution would have been to take the painting from its stretcher, which had never been done, and line it. He decided not to, at least for now. “I felt that it would be a terrible mistake for us all to cheer that this painting was so untouched and then, in the name of preservation, do everything to it,” he said. “The joy of working with a collection is that you don’t have to do everything today.”

Mr. Gallagher is a captivating speaker — “a born teacher,” Mr. Christiansen said. But he acknowledged that many conservators are ambivalent about how much to tell the public about their profession.

“A lot of conservators feel we shouldn’t be seen or heard,” he said. “We don’t want to reduce a collection to sounding like a graveyard, where every picture has a problem.”

The chief conservator at the Museum of Modern Art, James Coddington, said both in conversation and in the work he does, Mr. Gallagher has the ability to make a picture “come alive for you, to make it speak to you again. That’s in the end what we’re all trying to do: to get you excited about not what we do, but what the artist has done. And Michael does that.”