In the Harry Potter series, students are taught with different spells every year. When a student is in his or her 3rd year in Hogwarts School of Witchcraft and Wizardry, he or she will learn the Hardening Charm or “Duro” in Transfiguration class. This charm makes objects turn into stone. As per Hogwarts history, it was first taught and used in the school year 1986-1987.
It was used by Tulip Kurasu on a Jumbo Dungbomb as a prank on Barnaby Lee, Merula Snyde, and Ismelda. In the Harry Potter and the Deathly Hollows, to stop the two death eaters from following her, Harry Potter, and Ron Weasley, Hermione Granger cast Duro at a tapestry.
This was a tough one to guess. This was one of the last spells to show up in the movies. Hermoine used it in the Deathly Hallows in Battle of Hogwarts. Its also called the Hardening Charm