The wetsuits and tanks are stored away, the vessels sit at anchor and the winter routine of finding out what’s in the various concretions hauled up off the bottom each summer has begun.

In the lab of the darkened Whydah Pirate Museum, researcher and conservator Chris Macort sprayed distilled water onto what looked like a ragged lump of concrete you find on the buried end of a signpost.

Using a toothbrush and a dental pick, Macort slowly removed grains of sand that congealed around the contents of a pirate chest. These concretions were formed over the last 300 years by the electrolytic process of seawater and the iron of two pirate pistols. It was like mining in miniature, and Macort worked a seam of sand exposing gold and silver coins with crosses and other symbols standing like headstones in rows.

Shining like the sun through a film of oxidized iron was a chunk of gold, the size of a baby’s fist.

“Your eyes lock onto it when you see something that shiny and that yellow. There’s nothing else like it in the world,” Macort said. “Sometimes the gold just calls out to you, saying ‘I’m here, get me out of this concretion.’”

Pirate Sam Bellamy’s ship Whydah wrecked off Wellfleet in a violent storm on April 26, 1717, breaking into two or three large pieces, scattering its contents onto the sandy ocean bottom. Noble metals, like gold, are not reactive and don’t corrode. The gold that divers have been finding in the detritus scattered around the wreck site still seems like it’s come right from the smelter’s hand, immune to the ravages of the Atlantic through the intervening centuries.

“It’s right from wherever it was made, most likely Africa, or central South America,” Macort said. “The African gold has a little bit of a reddish hue from the copper in the sand.”

Macort said that divers working in a new area closer to shore found three concretions, including the one he was working on, that were alike in size, weighing about 40 pounds each with similar contents: coins, gold, two pistols and wooden fragments that are likely the remains of the chest.

From primary source research materials, he believes they are the individual chests that each pirate carried with him to store his share of the plunder. They would have weighed around 50 pounds, he believed, light enough for one man to carry, and the pistols were packed onto the top of the chest in case of trouble.

Those same primary source materials indicate there may be as much as 4.5 tons of looted treasure on board, Macort said. That includes gold dust used in transactions when the Whydah was a slaver before it was captured by Bellamy.

Whydah divers have recovered over 100 smaller concretions and 14 massive ones that weigh 3,000 to 9.000 pounds, often using specialized equipment to blow away a layer of as much as 20 feet of sand that has accreted over time.

“Because the iron (in cannons, tools, articles of clothing) is the common denominator, our metal detectors will scream before we get to within a few feet of (a concretion),” Macort said. They sit under the sand on the hardpan bottom, typically among the glacial erratics, stones that were dragged across the landscape and left behind during the last Ice Age.

“We’ve been trained to spot them,” Macort said. “The reality is that Mother Nature doesn’t make shapes like this.”

The concretions are X-rayed to give researchers an idea of what they contain. Sometimes it is something that may not be a precious metal, but the preserved remains of a pirate trapped in the chaotic debris of a shipwreck.

Barry Clifford and a team of historical researchers and divers found the wreck in 1984. For 23 years, Macort, himself a diver who works the wreck in summers, has been looking at a huge piece of concreted sand that only recently yielded the remains of a pirate.

Another concretion held the remains of John King, a boy estimated to be between 8 and 11 years old who was drawn to the pirate life and became trapped under cannons following the sinking. Preservationists were able to painstakingly separate a tiny black shoe with a silk stocking and leg bone from the rock-like accretion.

“(The concretion) was what saved the story and the remains of that little guy,” Macort said.