In 2015, teenage museumgoers created a time capsule of their own, adding e-cigarettes, a cellphone, a Starbucks cup and some concert tickets.
One of the museum’s richest sources of objects has been the Ear Inn, a house built around 1770 and still standing — although it has sunk 10 inches in the past 20 years — at 326 Spring Street in Lower Manhattan. Today, a bar and restaurant occupy its ground floor. The house produced many souvenirs of early New York when its owners, Martin Sheridan and Richard Hayman, dug up the basement.
“There’s a lot of great stuff in there,” Ms. Hofer said, “the objects of everyday life. It’s a snapshot of a time period and a class of people.” The haul included a chamber pot and whiskey jugs.
“We were digging in the basement to put in posts to shore up the house,” Mr. Hayman said. “The building has sunk six feet since it was built.”
A house doesn’t need Revolutionary credentials to be a trove.
“In my 30 years of architectural practice we’ve found many different things under floors and inside of walls, most left there inadvertently,” said Marvin J. Anderson, a Seattle architect. “Newspapers were used for years as insulation, and regularly help us date when an addition was built or an improvement was made.” In a recent renovation of a 1914 Seattle house, he found a layer of 1924 newspapers under the floorboards in a maid’s room.
“While renovating a 1902 house several years ago, we came across a fire-scorched red corset inside a wall,” he said. “It certainly stopped construction for several hours and raised many eyebrows, but we never figured out the story behind it.”
Some homeowners and some work crews choose to leave signatures and items behind as well, Mr. Anderson added. “When we renovate houses we encourage clients and their families to create and leave time capsules inside the house somewhere, something to be discovered when walls and ceilings are opened up in 50 to 100 years.”
Construction crews also routinely sign wall framing, knowing it will be covered up. “Years ago a client told me of the tradition of placing foreign coins under the basement floor slab; that it would bring wisdom from around the world into the home,” Mr. Anderson said. “I’ve never researched the tradition, but we’ve done this on numerous projects, as an opportunity to pause and celebrate a moment or milestone during construction.”
When Mr. Kennedy began working on Ms. Harrison’s 1816 house, a carpenter’s signature from 1921 was found on an attic window frame. Also discovered: a time capsule from the 1990s that included a note from the 9-year-old girl then living there.
Kim Gordon, a designer in Los Angeles who specializes in renovating 1920s-era homes, collects items she finds in the process and creates a small package she places in a wall when the project is done, sometimes with the owner’s knowledge, sometimes not. Inside a wall in a house from 1905, the oldest she’s yet renovated, she found a small sterling-silver medallion of the Virgin Mary, on a bit of chain. “It was very detailed, a beautiful, beautiful piece,” she said. After completing the renovation, she placed it into a small fabric pouch, added some crushed seashells, pebbles and a clay figure, and tucked it back inside a wall.
She collects small objects at flea markets “that speak to me” and keeps them for use in future packages during renovations. “It’s an anchor in the space,” she said. “I’ve given the house an intention.”
And, of course, commercial projects that require major excavation routinely unearth all kinds of things. But the 19th-century ship discovered in May 2016 in Boston, and the ancient elephant bones found in November of that year in Los Angeles during excavation work on the Wilshire/La Brea Station for the Purple Line Extension subway, were of jaw-dropping significance. The subway extension, a Skanska-Traylor-Shea project, produced teeth, tusks and a partial skull of at least two of the extinct mammals.
In Boston, another Skanska team at work on a 17-story office tower had been on site for more than eight months, and was six to eight weeks into the excavation phase when it revealed a ship, sunk between 1850 and 1880, that still contained barrels of lime and items including knives, forks and plates. It was about 20 feet down and approximately 500 yards from the current shore by the Institute of Contemporary Art.
It’s in “the heart of Boston and the heart of a major development” said Shawn Hurley, the chief executive and president of Skanska USA commercial development. “We didn’t know what it was at first, but the employee who saw it was smart enough to stop construction.”
It was a sunny day. Skanska’s offices overlook the site and excitement grew as staff members realized, “We’ve got the real deal!” he recalled.
Suddenly encountering a piece of history can be a shock.
“I felt kind of amazed. I’ve never seen anything like it,” said Mr. Hurley, who then immediately faced a host of questions: “What do we need to do here? What are the next steps?”
The importance of their accidental find was confirmed, he said, as city and state archaeologists agreed it was the most significant find of their careers. “We probably had a team of seven or eight archaeologists on-site for a week. They were ecstatic.”