Hippocrates’s dictum Ars longa, vita brevis could be applied to the work of modern art conservators and preservers. Like surgeons trying to save a life, the conservators and preservers at New York City museums dedicate themselves to ensuring the longevity of works of art for public view.

The chief conservator at the Museum of Modern Art, Jim Coddington, is currently working on restoring Matisse’s “The Piano Lesson.” An average day for him includes dusting, checking light levels, and ensuring proper storage.

For his team, the first step in conserving a work means looking at the materials. “When we encounter a new material, or new combination of materials, we first try to understand what they are,” Mr. Coddington said. “The source of this information might be the artist or prior correspondence with the artist, or perhaps conversations with curators or colleagues who are familiar with the particular artist’s work.”

Treating a work is both a curatorial and a conservation issue. “If a material is chosen precisely because it does change and perhaps ultimately decays,” Mr. Coddington said, “how do we honor that intention and keep the work alive as long as possible?”

Artwork takes several paths to restoration at MoMA, Mr. Coddington said. Routine checkups take place when a piece is being readied for an exhibition. Surface cleaning takes about a day, while works that require in-depth work, such as “The Piano Lesson,” can take months to be completed.

According to Mr. Coddington, “The Piano Lesson” has been a reasonably straightforward treatment. The first step was to remove dirt and grime from the surface with a water-based solution. Then the synthetic resin varnish was removed with organic solvents, and Mr. Coddington began to retouch, a process that consists of “filling the loss area to the level of the original paint and then matching the color of this fill to the surrounding original,” he said. He uses readily removable paints and is limited to the area of lost paint.

Conservator Margaret Holben Ellis recently published an essay on the artist Jackson Pollock’s materials and techniques, for “No Limits Just Edges: Paintings on Paper by Jackson Pollock,” a catalog accompanying a 2006 exhibit of the same name at the Guggenheim Museum.

“Pollock’s works on paper are surprisingly sturdy. Most of the damage happened after their creation, either in his own studio, the Springs, or by subsequent owners,” Ms. Holben Ellis, a professor of conservation at the Institute of Fine Arts at New York University and the director the Thaw Conservation Center at the Morgan Library & Museum, said.

At the Morgan, Ms. Holben Ellis often is confronted with the challenges of preserving modern papers, including newsprint, carbon copies, onion skin, tracing paper, faxes, and construction papers. Drawing and printing media complicate the work: She has worked with ball point pen, Magic Marker, Day-Glo paints, and mimeograph ink, on material held together with Scotch tape, rubber cement, and Elmer’s glue.

The Morgan, for example, owns the complete manuscript and drawings for “The Story of Babar,” Jean de Brunhoff’s 1930-31 children’s book about an elephant king. It also owns drawings in various stages for “Babar’s Cousin: That Rascal Arthur” (1946) by Laurent de Brunhoff, who wrote many Babar books after his father’s death.

“Conservation problems included the removal of rust stains from paper clips, a 19th-century invention, adhesive stains, and various registration marks made in the course of preparing the manuscripts for publication,” Ms. Holben Ellis said.

The Babar project involves collaboration with conservation fellow Denise Stockman and a Morgan curator of literary and historical manuscripts, Christine Nelson. “Because Laurent is still living, we were able to consult him about some small points in the treatment of the Babar materials,” Ms. Nelson said. “Decisions had to be made about whether to remove certain kinds of tape and other markings.”

Ms. Nelson said such decisions are the most interesting parts of the conservation process. “I don’t think most people realize how subjective many treatment decisions can be. What kinds of marks does one try to remove or lighten, and which should remain as part of the history of the manuscript? Which holes and tears does one fill or mend, and which remain as evidence of the ephemeral nature of preliminary work?”

The Thaw Conservation Center is also working on an artwork by Richard Lindner, which Ms. Holben Ellis describes as “four small pencil drawings arranged on a sheet of loose-leaf notebook paper using 11 now severely degraded and distracting squares of Scotch tape.”

The team must decide whether all traces of the Scotch tape should be eliminated, whether each piece should be replicated using a similarly shiny plastic film, or whether the tape should simply be left alone. Most of the damage has already occurred, based on what Ms. Holben Ellis calls “the aging curve” of the rubber adhesive.

“We would not remove the tape without documenting its existence,” Ms. Holben Ellis said. “Sometimes aesthetic issues come into play. Some artists quite like the look of curled and yellowed, aged Scotch tape. For example, for a collage that one of my students treated, Robert Rauschenberg requested that the aged tape be preserved in situ or replicated.”

As for Babar, he will be on display at the Morgan in a future show, accompanied by his cousin, the rascal Arthur.