Agatha Chubb is an expert in ancient wizarding artifacts. While researching Quidditch practices of the 16th century, she recovered no fewer than 12 lead Bludgers from marshes and peat bogs in Great Britain and Ireland. She used this discovery to demonstrate how modern wizards developed Bludgers from lead and then iron, as lead was determined too soft a metal for the purpose of the balls.
She wrote, "They are undoubtedly Bludgers rather than cannon balls. The faint indentations of magically reinforced Beaters' bats are visible and one can see the distinctive hallmarks of manufacture by a wizard (as opposed to a Muggle) - the smoothness of line, the perfect symmetry. A final clue was the fact that each and every one of them whizzed around my study and attempted to knock me to the floor when released from its case."