Ongoing restoration work being done to the Washington Monument in the Mt. Vernon neighborhood of Baltimore has turned up an unexpected find. Workers discovered a 100-year-old time capsule, and officials hesitate to open it because they are concerned with the age of the contents and the prospect that they may be delicate.

The Mount Vernon Place Conservancy says that the capsule will be moved to the Walters Art Museum nearby where conservators will determine when it may be safely opened after assessing its condition. Officials fear that the contents may have suffered from exposure to dampness within the monument, resulting in decomposition of the contents.

Robert Mills who also designed the larger and newer Washington Monument that adorns the National Mall in the nation’s capital designed the Mt. Vernon Washington Monument. Building began in 1815, and the monument was completed in 1829.

The capsule is a sealed copper box that was held behind a plaque commemorating the monument’s centennial, September 12, 1915, which corresponded with Defender’s Day, a legal Maryland holiday honoring the successful defense of the city of Baltimore on September 12, 1814, from an attack by the British. It was discovered during an investigation by restoration project superintendent George Wilk II into how the plaque was secured to the wall.

“We were hoping that the plaster in the niche might give us clues as to the appearance of the original plaster in the museum room,” Lance Humphries, chair of the conservancy’s restoration committee, said in a statement. “Little did we realize that there was an actual time capsule stashed behind the plaque.”

Experts speculate that the capsule contains copies of The Sun newspaper, commemorative programs, and other relevant material.