There's no doubt that the pair of apparently gold-mounted black onyx pendant earrings are old. But there is doubt that they were ever owned by former first lady Mary Todd Lincoln. Yet the Kentucky Historical Society, as part of the state's Abraham Lincoln bicentennial celebration, has been displaying and publicizing them as hers. Acquired at auction in late 2008 for more than $19,000, the earrings' provenance may need to be proven by a missing photograph...