The image above was published in Archaeology magazine last year. It's a neutron-beam-generated image of a lead shot from the Mary Rose shipwreck, showing a fragment (?crystal) of iron inside the lead coating. I found more details at The Telegraph:
Among the items most exciting archaeologists are cannonballs believed to be early examples of armour-piercing rounds. Such shells were thought to have been developed during the late 1800s, before the technology was refined during the world wars. But the new findings by experts working with the Mary Rose Trust, which has been preserving the ship, now suggest the technology was being used several centuries earlier — although it could also have been a money-saving strategy, using cheaper iron inside the lead balls.Image credit: Bob Cywinski, University of Huddersfield.