She can craft jewelry from silver, gold, titanium, and—when the occasion demands it—a White House magnolia treeIt’s no surprise that a tree stump sits in the corner of Kara Ross’ light-filled Manhattan showroom. The designer—whose fine jewelry is known for large-scale geometric patterns and unusual materials, including wood, jet, and volcanic lava—isn’t afraid to mix and match decadent gems with humble organic matter. But this log is no ordinary kindling: Ross received it on spec from the White House.“The president and first lady wanted unique pieces to give to visiting heads of state, and after seeing some of my jewelry made of maple and diamonds and gold, they contacted me,” Ross says. Taken from a magnolia tree originally planted by Andrew Jackson, the wood was used to make bracelets and engraved trays presented as gifts to represent the United States. “It’s a wo