Gouging chisels are recognized by their "smile" or amount of bevel cast into the end. There are two basic types of gouging chisels: firmer and paring. A firmer gouge is used to dig out broad swaths of material, usually with the assistance of a mallet striking the butt of a chisel. A paring gouge is smaller and finer, and is used to remove material to bring out detail in the piece. Either type will eventually become dull with use. Sharpen a gouge chisel in a different manner than a flat chisel because of the curve of the bevel. Use the same tool to sharpen the gouge chisel, but you'll need to learn a slightly different method of using it.
Hold your gouging chisel by the handle so the top of the chisel is facing up.
Use a round edge fine whetstone to sharpen the inside of the bevel curve. Hold the whetstone along the top of the handle, down at a 45-degree angle to the edge of the bevel. Push and pull the whetstone over the edge quickly. As you do this, slowly move the whetstone from side to side on the blade, moving it back and forth over the edge. Do this for several minutes until that edge is sharpened.
Turn your gouging chisel over and use the rough whetstone to sharpen the back of the blade. Hold the whetstone at a 45-degree angle to the edge of the chisel and move the stone back and forth quickly while also working it from side to side. Do this for several minutes until that edge is sharpened.