The scanner in David Williams's lab is built to look inside bones. This time the object on the table was a small brass padlock that had stayed shut since 1583.
The lock came from the Ann Francis, a merchant ship wrecked in a storm on the evening of December 28, 1583, on Margam Beach in Wales. Researchers think it once closed a chest on board, then became separated from whatever it was protecting. When Peter Hughes found the lock in 1999, while walking the beach with a metal detector, the letter rings still turned after centuries under the sand.
He tried the combination for about 20 years and never hit the right four letters. The lock has four rings, and each ring carries six letters, which makes 1,296 possible codes. Extra letters on the ends do not move, as if they were placed there to confuse a thief. After National Museum Wales acquired the lock, staff could hear grit inside the dials, and forcing the rings risked harming an object that had already lasted four centuries.
This month the museum and Cardiff University said they had found another way in. Williams used micro-CT scans, which take thousands of X-rays and build them into a 3D picture, so he could see the mechanism without breaking the case. He matched the notches inside to the letters outside and read the code: ANCE. He then had to wait until later that evening for museum staff to line up the four letters. When the message came, the lock had opened.
"We normally use this technology to study bones and other biological structures, so investigating a 400-year-old padlock was certainly a first for us," Williams said. Alastair Willis, a senior curator at the museum, said locks of this kind are known in Britain, but few survive in such good condition and with a dated wreck beside them. "Of course, now we've solved it, we are left wondering if the code meant something to its owner."
The four letters now sit in the open, still carrying whatever private meaning a person on that ship once chose.