To take a block of ice and sculpt it into art, you need a few things. A chain saw, some customized tools and a Zen master's grasp of impermanence. In a nippy parking lot off of Delmar Boulevard in the Loop on Saturday, Sean Leahy wielded a Stihl MSE 180 C and deftly buzzed through a 300-pound block. He wore heavy ski pants to seal off the cold, but only thin cotton gloves to give him a better grip on the ice. He heaved the pieces around or pushed them along the ground with his hiking boots, then sliced some...