Black powder like this, one of the earliest explosive materials, is sensitive to heat, shock and friction even when newly made. But if subjected to water and then dried, it can become much more sensitive and the risk of an explosion increases. The Richmond Police Department’s bomb squad arrived, took the explosive core away and blew it up on a demolition range. “Then we found three more in other boxes,” Blake said.

After another call to the bomb squad, the two conservators began a monthlong search through their storeroom and ended up finding two dozen black powder cores from the wreck of the Betsy.

Munitions like these often far outlast the conflicts they are used in. Ridgway, Blake and police bomb-squad officers had a tricky situation to deal with. Their museum is not alone in having this kind of problem. “I’ve worked at other museums where we found muskets that were loaded, museums with loaded cannons, percussion cannonballs and other ordnance from the Civil War,” Ridgway told The Times. “I’ve probably worked with five or six different military E.O.D. teams and police bomb squads.”

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In some parts of the country, where police and fire departments do not have their own bomb squads, military explosive ordnance disposal (E.O.D.) teams are called to respond. While the Army, Navy, Marine Corps and Air Force all have E.O.D. teams, only Marine E.O.D. technicians as a whole are trained and equipped to take live munitions and “inert” them by safely removing explosive material in a way that preserves the rest of the weapon.

Marines are sometimes asked to visit museums and inspect items that conservators suspect may be live munitions. Whenever possible, they inert these items and return them along with paperwork that certifies they are safe for public display. “It’s easy to spot a grenade in pristine museum condition, but in archaeological conditions, it’s rarely that easy,” Blake said. To help, she and Ridgway are working on a guidebook that they plan to distribute free.