THE white and gray pigeon lit on one corner of Brig. Gen. Thaddeus Kosciuszko's bronze hat, then moved to the other corners of the hat, and roosted finally in the crown, more than three stories above the Lafayette Park lawn.When the general has been visited by enough pigeons, it is time for Nicolas Veloz and his secret formula for fighting pigeon litter. Mr. Veloz is the man responsible for the maintenance and cleaning of some of the most important statues in the Washington area for the National Park Service. Several years ago he discovered a formula for cleaning so innovative, successful, but improbable at first, that it defies credibility. He uses walnuts. It happened this way: One day in 1978 he was out in his driveway, experimenting with what they call in the business "abrasive cleaning." He suddenly thought of a trip he'd made in high school on Armed Forces Day to an Amarillo, Texas Air Force base. "I remembered they said they cleaned the inside of jet engines with ground walnut shells. They'd start the engines, get a bucket full of walnut shells, throw 'em up in the air, they'd get sucked in on the intake, fly around on the inside, get blown out the back end with all the soot and dirt and crud from the engine. "And I thought, well if it works on aluminum and all the stuff that's soft and lightweight and jet engines, it might work on bronze. I had tried different abrasive media, I'd tried grass seed and hominy grits and corncobs, so I got some walnut shells. "I had bought a soda-acid fire extinguisher that was corroded at a yard sale. It was made of soft copper, softer than bronze, and I figured if it takes off [the buildup of corrosion] on copper maybe it will work on bronze. So I tried it with this portable sand blaster in my driveway at home, blasting the fire extinguisher with walnut shells. It worked." Within the year they tested the process on a statue of Admiral Byrd on Memorial Drive at the entrance to Arlington National Cemetery. The admiral was as white as though he'd just stepped out of a North Pole blizzard before Veloz blasted him with walnuts. "And it worked on Byrd," says Veloz, who has pictures of the amazing before and after in which the admiral positively gleams. Nick Veloz is a compact-looking man with a sandy beard and hair; his horn-rimmed glasses mask the intensity of his eyes when he's talking statues and how to clean them. I remembered the Byron poem "Childe Harold To the Dark Tower Came" when I tried, in vain, to get into his office in a round, black stone tower above an art gallery at Glen Echo Park in Maryland. The gallery was closed, so we met instead at a National Park Department office nearby where he is cultural resources management specialist for the National Park Service. He works within the National Capitol Region and is assigned to the George Washington National Parkway where his next assignment is the Iwo Jima Memorial statue. But because of his expertise he has traveled widely, cleaning up some of the nation's most historic monuments at Valley Forge, Shiloh, Fredericksburg National Battlefield and others. "Battlefields are where most of the statues are," he says. He's also worked on statues in other parks: The President's Parks, the Ellipse, and Lafayette Park with its four corner statues facing the White House. MacPherson Park with its statuary, he says is one of the densest sites for pigeon guano. "They hold conventions there." Pigeons not just on the grass, alas, as Gertrude Stein might have put it. The worst statue disaster area in terms of birds (pigeons as well as gulls from the not-too-distant Tidal Basin) is the Boy Scout monument on the Ellipse, says Veloz. Parks officials keep tabs on two gulls named Heathcliffe and Gertrude, who stop there on a regular basis. For the past 15 years Veloz has trained people with the Park Service here in Washington in the art of maintaining federal statuary. He also travels around the country to clean and maintain the private statues. He's in demand because of his well-burnished reputation. When they needed an expert to bring Saint-Gaudens's famous statue of Henry Adams's wife back to its former glory, they called Nick Veloz to the Rock Creek Cemetery where it rests. The statue, dubbed "Grief" was commissioned by Adams after his wife's death. Veloz used the same ground walnut shells to blast that statue back to its original beauty. The walnut shells are ground up so finely they look like curry powder, and the faint scent of walnuts lingers. He uses the ground walnut shells in a sandblaster at between 20-25 pounds per square inch pressure, a fraction of the 125 pounds pressure (per square inch) the Park Service had employed to clean statues using tiny glass beads that was the common method in the '70s. Tests have since proven that the beads and higher pressure were causing the sort of damage to bronze that sandblasting with walnuts doesn't. A former archaeologist and geologist, Veloz likes to quote the great art critic John Ruskin: "Take proper care of your monuments and you will not need to restore them." His method for doing that is first to wash the statue "until basically things are clean as far as birds go" and anything else that would attack bronze (like pollution) is removed. "I wash the statue in detergent and water, [sometimes drying it with diapers] blast it with walnut shells, treat it with a corrosion inhibitor and give it three coats of wax. We use a mixture of several different waxes, rather than a clear, painted coat because most of the clear coatings give an unnatural sheen and it's difficult getting them off." How long will a statue last with that treatment? If you wash it down and wax it once a year, Veloz says, it will never need to be treated again.