This video walks you step by step through the process of fine tuning a chisel to perform at its best. The sharpening techniques shown can also be applied to hand plane irons. His technique is meticulous, but once understood, will save you time and give you a fantastic tool.
No matter how sharp the edge of the chisel, it will never perform to its full potential if the back of the chisel isn’t flat. In order to have a flat chisel, you must also have a flat stone. Many woodworkers begin by using water stones. These are manufactured sharpening stones available in varying grits from as low as 400 all the way up to 8000 grit. Water stones are great to work with a have a pretty easy learning curve. Their one major downside is that they can become dished over time. This means that the middle is worn away more than the two ends. It is necessary to periodically check the flatness of your water stones. A water stone may be flattened by rubbing it on a piece of sandpaper placed on top of a flat glass plate. It is worth the time to make a grid of pencil lines across the face of the water stone so that you may track your progress. Continue rubbing the stone across the sandpaper until all pencil lines have been removed. Remember to use water and continually flush the slurry off the sandpaper as you flatten the stone.
One way to avoid working with a dished water stone is to instead use a diamond sharpening stone. This is a large, flat steel plate embedded with industrial diamonds. Due to the hardness of the diamonds and the steel plate, the diamond stone does not become dished. The downside of using a diamond stone is that it is more expensive and can rust if you do not dry it thoroughly after use. One technique is to use a diamond stone primarily for flattening chisel and plane irons and then using several water stones for honing the bevel. A slightly dished water stone will have little impact when used only for honing the bevel on the face of the chisel or plane iron.