Standing on a scaffold platform 180 feet above the Capitol's rotunda, Bernard Rabin is ready to begin carefully cleaning the fresco. All he has with him is a bucket full of solution -- really just water and some mild softeners -- and a sponge.

He will begin with a section under a figure representing freedom and work his way around, taking pictures and chemical tests before dabbing away the dirt, smoke and grime that have collected in 122 years.

"It's a magnificent way to end a career," said Rabin, 70, who has been a conservator for 45 years. "I've never worked on such a large project as this or {one} as historically important to the United States."

There is 4,664 square feet of restoration work to be done on the fresco, "The Apotheosis of George Washington." Some days Rabin cleans 20 square feet; others, a single square foot. He has given himself 16 months to complete the project. The man who painted the fresco, Constantino Brumidi, completed his job in 11 months back in 1865.

Rabin has been given a triple task: to clean the fresco, remove the work of an earlier restorer, and paint sections that are missing. The object is to return the work as near to its original state as possible.

To the viewer below, the fresco appears to open up to the sky. It depicts George Washington surrounded by mythological and historical figures.

Between the ministrations of Brumidi and Rabin, a restorer named Alyn Cox worked on the fresco in 1955, but only ended up blunting the effects of Brumidi's work. Cox ended up highlighting cracks that were meant to be invisible.

Rabin can take advantage of techniques and technology Cox did not have, but still will have to improvise and rely on his instincts more often than not.

When Rabin mistakenly dabbed away a small section of green paint, he used his first-aid gauze pad to figure out whether the paint was by Brumidi or Cox. He found out it was Cox, and therefore rightly removed.

"Rabin is an esteemed fresco conservator and well respected in the field," said Ann Hoenigswald, acting head of painting conservation at the National Gallery of Art. "He is experienced in working on large projects."

But Rabin, who has examined the fresco six times during the past four years in preparation, said he is overwhelmed by the project and called it "mind-boggling."

Rabin's day begins with a seven-minute elevator ride to the top of the scaffold. He decides then what to do and who will work where.

Photographs of work to be done and work completed are taken to study and compare for the next section to be restored. Chemical tests are done continually as work progresses.

At 4 p.m., Rabin and his two assistants descend to discuss what has been done and plan for the next day.

In August, Rabin and his crew will be joined by two Italian experts on mural conservation who will act as advisers.

Until the work is completed, visitors will not have a view of the fresco or the conservation work in progress.

A north-south passageway will allow people to move from one side of the Capitol to the other, and tour guides will explain the restoration process to visitors.

Because of the Capitol's air conditioning, which acts as a filtration system, the completed restoration is expected to survive better than Brumidi's, which suffered from exposure to pollutants.

Smoke from 500 gas lights around the rotunda, as well as humidity and dust from the outside when the doors were opened accumulated on the fresco, giving it its dull appearance, Rabin said. "We have pollution control now," he said.

While restoration work is beginning on the fresco, scaffolding for work on the exterior west front of the Capitol is being taken down.

After three years and nine months, the restoration project that has been obscuring the view of the Capitol's west facade is nearly complete.

The project will be completed by late August or early September, 10 months early, a spokesman for the Architect of the Capitol said.