Jeff Johnston crouches low with his hammer and chisel, tapping patiently at what looks like dirty concrete surrounding a piece of rusted iron.
Bang, bang, bang, his hardened-steel tools sing, the sound rising up from the bottom of a deep 20-foot-wide shaft that resembles a giant mineral-encrusted water main.
For eight weeks now, Johnston and his fellow archaeologists have battled this stubborn material for hours at a time, laboring to unlock the secrets of one of history's most famous warships. Four hundred artifacts have emerged from its grasp so far, including a cache of officers' table silver, as well as shoes, buttons, pocketknives and the remains of two long-dead sailors.
Less dramatic but equally important is the slow materialization of the walls, roof and other structural features of this celebrated Civil War milestone. Only now are their original surfaces beginning to appear, after more than a century of marine encrustation and corrosion.
"The longer you stay in here - and the longer you look around - the more things you start to recognize," Johnston said Tuesday, taking a break from his work at The Mariners' Museum.
"It's really starting to look like we're inside the gun turret of the USS Monitor."
Recovered from the Cape Hatteras, N.C., wreck in early August, the Monitor's revolutionary iron turret has been the focus of an intensive archaeological investigation led by scientists from the Monitor National Marine Sanctuary and the museum.
Made up of a four-member team of excavators - and supported by what sometimes seems like a small army of sediment screeners, conservators and other helpers - the archaeologists have removed tons of coal, coral and silt from the turret since they started. But no one realized when the work began how difficult it would be to reach the bottom.
Working on their hands and knees into the night, the excavators extracted the last of the human remains in September. Then and now, they say, hammering through the concreted rust and coal in search of artifacts has required stamina and patience.
"We're running into lots and lots of coal - all the way down to, and then in between, the roof rails," Johnston explained. He's a Civil War naval historian who's become one of the leading authorities on the construction of the pioneering ironclad vessel.
"The problem is that some of the worst spots are in the last few inches. That's where all the good stuff has been found - and that's where the concretions really get tough."
After nearly 140 years at the bottom of the Atlantic Ocean, the thick iron walls of the turret are loaded with unstable chloride salts. So they must be flooded every few days to stave off the potentially catastrophic effects of a reaction with the atmosphere, which could cause the historic armor plates to expand and crumble.
That dire threat has reduced the number of days when the archaeologists can crawl down a steep ladder into the giant 70,000-gallon conservation tank - and even then, they must work in a dripping mist produced by a special system of irrigation hoses.
With 28 days of digging behind them, however, the scientists have cleared nearly half the turret, which tumbled upside down and landed on its roof during the ship's violent Dec. 31, 1862, sinking during a storm. They've also found scores of artifacts that have shed light on the tragic last moments of the stricken vessel.
Among the most poignant objects recovered is an intact lantern that might have been used to light the turret's interior on the night the Monitor went down.
Equally moving is the discovery of more than a dozen silver forks and spoons from the officers' mess, three of which can be linked by identifying marks to the unfortunate owners.
"Two of the pieces have initials that can only be tied to a single person. The third is a flat-out certainty because it actually has a name," museum collections manager Jeanne Willoz-Egnor said.
"The sad thing is that none of them made it."
In addition to finding these evocative personal effects, the excavators have uncovered numerous gunnery tools, including a shot ladle and rammer head that were used to load and fire the Monitor's powerful battery of Dahlgren cannon.
Both of the huge 15,750-pound barrels remain in the turret, resting in the topsy-turvy positions where they landed when the doomed ship slammed into the ocean bottom.
Still visible on top of the portside gun is part of a celebratory inscription engraved after the Monitor's momentous March 1862 clash with the CSS Virginia - also known as the Merrimack - in the history-making first Battle of the Ironclads in Hampton Roads.
And it's that kind of fragile evidence that the archaeologists hope to preserve by continuing to work with patience and persistence.
"One of our big jobs after we're done here is going to be getting these cannons out," said John Broadwater, chief scientist and manager of the Monitor sanctuary.
"They're well-cemented in here - right down to the roof beams - and we have to decide if we're going to remove these massive gun carriages at the same time. So it's all going to depend on what we can do with the least amount of trauma to the artifacts."
Mark St. John Erickson can be reached at 247-4783 or online at firstname.lastname@example.orgCopyright © 2015, Los Angeles Times