It's been puzzling art curators and experts for a long time, but scientists at the University of Antwerp discovered the reason why some of van Gogh's most prized works of art are turning white.
FROM THE NEWSROOM: At the top of the agenda for The World today, Iraqi troops are making headway in their battle to take back the city of Tikrit from ISIS control. We've got an update on that. Also, Thomas Erdbrink of the New York Times has been gauging reaction in Tehran to the news that a group of GOP senators have sent a letter to Iran cautioning against a nuclear deal with the US.