From the beginning, Matthew Fallon was drawn in by color.

"Glass is something that lives in light. And when light hits a glass that's been designed by a master, it does something hard to describe. The color is very, very powerful," Fallon said.

A Somerville resident, Fallon brings stained glass windows back to life. As one of two workers who paint glass for Serpentino Stained & Leaded Glass, he helps restore damaged and dirty glass masterpieces from such places as the Hall of Flags at the Massachusetts State House, Boston's Trinity Church, and the Christian Science Plaza, including glass in the Mother Church, the Mother Church extension, and the Mapparium.

Fallon, 47, studied filmmaking at the Massachusetts College of Art in Boston. He started working with stained glass as a hobby around 1979 and got his first studio job in 1983.

In stained glass, there are generally two schools of color: the medieval style, which emphasizes blue and red on transparent glass; and the opalescent style of the late 19th century, which uses many more colors on milky, translucent glass.

Fallon, who works in both styles, began painting glass seriously around 1996, when he began studying with a master glass painter in New Hampshire. It is a highly technical skill.

"Glass, it's a unique material . . . Many artists compare it to painting on air," Fallon said. "It's almost intangible the delicacy, the brilliance of the color."

A window begins with a piece of glass, either clear or colored. An artist paints an image on the piece, which is then fired in a kiln so the paint is sealed. The panes of glass are held together in the window by strips of lead.

Stained-glass windows are made to last. Artists and restorers tend to speak in terms of centuries, but problems inevitably develop over time.

Portions of a window can deflect, a term used in the business meaning to bow, bend, or buckle, if the leading doesn't provide sufficient support or if heat builds up in an area that isn't properly vented.

As glass expands because of temperature, the lead expands with it, but as glass contracts, the lead does not, which can leave gaps between the glass and the leading. Lead also eventually deteriorates.

Ultimately, a piece of glass may crack or fall out. Stained glass can also get dirty. Sometimes owners even paint over them.

Restorers remove windows intact and take them to the studio. They document them with photographs and rubbings made on acid-free vellum with a rubbing stone (made of wax and crayon) or carbon paper.

The rubbing provides a sort of full-scale map of the window. Information is also recorded on the width and types of lead.

Then the windows are disassembled, and each piece of glass is cleaned. Cracked pieces are glued together using silicone, epoxy, or copper foil. The panes are then put together again using new lead, if necessary, or the original lead if possible.

The painstaking process of restoring windows takes months. At any one time, Serpentino's, whose workshop is in Needham, is working on six to eight projects.

A glass painter typically starts by applying more paint than needed. Then, to accentuate the effect of the sunlight, some of the paint is removed. It's essentially the opposite of a canvas painter, who adds highlights by adding paint.

"With glass, you're removing the highlights," Fallon said. "You lay on the paint and then scratch away."

Painting is a last resort in stained-glass window restoration, because the goal is to preserve as much of the original work as possible. But sometimes a glass piece is missing or damaged beyond repair, so the restorer must re-create it in essence, to figure out what the original artist intended.

Arthur Femenella, a stained-glass consultant and conservator who often refers projects to Serpentino's, said that while there are probably a few hundred companies in the United States that work with stained glass, there are fewer than 20 that do the sort of high-quality restoration work Serpentino does.

"We were very pleased with their work. Their work was careful and thorough," said Alan Spence, capital project manager at The First Church of Christ, Scientist.

Mindful that his art is from a bygone era, Fallon is proud that he doesn't own a car. During good weather, he rides a bike to work, which takes about an hour and 10 minutes. During the winter, he relies on public transportation, which includes a bus, two trains, and a half-hour walk. The journey takes about two hours each way.

"It factors into the whole medieval aspect of the trade," Fallon said. "I live in the past a little bit."

Indeed, that's required by what he does for a living.

"Preservation is a very gratifying activity, I think," he said. "I just think the past is invaluable. There's so much we can learn from the past, and the past is disappearing so quickly. The more we can hold onto, it's better for everyone."