Chisels need to be very sharp, so use an extra fine stone such as a flat carborundum stone. Lay it flat on the bench, and at right angles to the body. Use a light cutting oil to lubricate and provide the cutting medium. The chisel initially abrades away a small amount of stone which combines with the oil to, in turn, abrade away the blade. The chisel is held at a set angle, usually 25 degrees for the backing edge, and 30 degrees for the cutting edge.
To get the angle correct, it is worth purchasing a honing guide, which is a small tool that clamps onto the chisel and holds it at the required angle. Grasp the chisel in the right hand, with the forefinger pressing down on the flat of the steel. The motion is straight back and forth, towards and away from yourself.
Work gradually over the whole surface of the stone, to avoid hollows forming. Only the oblique side of the blade is honed. Take care to hone the end square. It is easy to press slightly harder on one side of the chisel than the other, by placing the forefinger off-centre, which results in one corner being ground too hard and a cutting edge not square to the axis.
Honing will raise a metal burr on the back of the blade, which is then removed by reversing the chisel so that the back is resting flat on the stone. A short, circular rubbing motion will remove the burr.
In extreme cases, where a chip has been taken out of the cutting edge, or where the cutting edge is no longer square to the rest of the blade, regrinding will be necessary. This can be done using a coarse oil stone in the method described above, but is hard and long work. A water-cooled sandstone grinder makes the job a lot easier. An adjustable tool rest can be used to hold the chisel at the correct angle to the grinding wheel. Use very light pressure as the chisel is moved to and fro across the wheel so grinding the blade evenly, and giving even wear on the stone.
If using a grinder that is not water-cooled, great care must be taken not to overheat the end of the chisel or it will lose its temper, i.e. become soft and no longer hold an edge. After two or three seconds of grinding the chisel should be dipped in cold water for a few seconds. Then inspect the blade, and repeat as necessary.
After grinding, the blade should be sharpened as described above.
