Place a column, texture side down, in a well in a wood swage block that is less curved than desired. Place a corresponding wood dowel on top of the column and hammer with a plastic mallet. Move the metal column to the next smaller depression and repeat the process. Continue until the desired curvature is achieved.
Pro Tip: Cut various size dowels, available at any hardware or craft store (or my wood shop) to fit the depressions in the swage block.