Crews worked carefully on Thursday to remove a time capsule dating back to 1795 from the granite cornerstone of the Massachusetts statehouse, where historians believe it was originally placed by Revolutionary war luminaries Samuel Adams and Paul Revere among others.

The time capsule is believed to contain items such as old coins and newspapers, but the condition of the contents was not known and the Massachusetts secretary of state, William Galvin, speculated that some could have deteriorated over time.

Originally made of cowhide, the time capsule was believed to have been embedded in the granite cornerstone of the building when construction on the state Capitol began in 1795. Adams was governor of Massachusetts at the time.

The time capsule was removed in the mid-19th century and its contents transferred to a copper box, Galvin said.

Paul Revere, American patriot and silversmith, is believed to be among those who placed the time capsule. Photograph: Hulton Archive/Getty Images

It is being removed now because of an ongoing water filtration project at the building.

The time capsule will not be immediately opened but instead taken to Boston’s Museum of Fine Arts, where it will be x-rayed to determine its contents.

Pamela Hatchfield, a conservator at the museum, slowly chiselled away at the cornerstone on Thursday to reach the box, a process that was expected to take several hours to complete. Galvin said the plan is to return it to the site sometime next year.

The excavation comes just months after another time capsule was uncovered from the Old State House, which served as the state’s first seat of government. That long-forgotten time capsule, dating to 1901, turned up in a lion statue atop the building and when opened, was found to contain a potpourri of well-preserved items including newspaper clippings, a book on foreign policy and a letter from journalists of the period.