How to Sharpen a Knife

How to Sharpen a Knife

A knife is useless if it is not sharp. You can tell if your knife is sharp if it can cut a soft ripe tomato into thin slices with ease. If the knife is dull, it will just crush the tomato.

If you looked at the cutting edge of a knife through a magnifying glass, you'd see that it is made up of hundreds of tiny teeth-like a saw. Through repeated use, these teeth get twisted and bent out of alignment. This is what makes a knife dull; a sharpener gets these little teeth back into alignment.

The harder the metal the knife is made of, the harder it will be to sharpen, but the longer it will hold its edge. A sharpener has to be made of a material that's a shade harder than the metal it is to abrade. (The hardness of metals is measured on the "Rockwell Scale.")

"Steels" are metal sharpeners. They have a fine grain and give a super finish to an already sharp knife. Butchers and professional cooks use a steel constantly, giving the knife a few strokes before each use. A ceramic sharpener is better than a steel for sharpening hard metals such as stainless steel. (Ceramic is harder than the hardest metal on the Rockwell Scale.)

Eventually, repeated sharpening wears away the little teeth of the cutting edge. At this point the knife needs to be ground to thin the blade into a new cutting edge. This is done with an abrasive stone.

Using a Ceramic Sharpener

1. Start with the heel of the blade at the tip of the sharpener and slide the knife down the length of the sharpener so the cutting edge abrades against it. Apply steady and strong pressure. Keep the knife at the same angle constantly.

2. End with the point of the blade near the base of the sharpener. This is one steady stroke, one hand moving toward the other, every inch of the cutting edge making contact with the sharpener. Repeat on the other side of the sharpener to sharpen the other side of the knife.

Using a Steel Sharpener

3. When using a steel sharpener to sharpen high-carbon-steel knife, start with the heel of the blade at the base of the steel and pull the hands away from one another, finishing with the tip of the sharpener at the tip of the blade. Make sure that the whole blade gets worked against the sharpener. Keep the angle about 25 degrees and the pressure the same.

Using a Grinding Stone
4. Once a year, twice a year, once every two years-depending on the kind of beating your knives get-you will need to grind them down to form a new cutting edge. You can send your knives out and have them ground by a professional or you can do it yourself if you have a sand wheel or a large stone like the one pictured here. This stone is held in place by suction so that you can apply a lot of pressure without having it slide around the way smaller stones do. It has three sides, each of a different coarseness. You begin with the coarsest side and finish with the finest.

5. Rub some mineral oil on the stone to keep stone grindings loose so they can be wiped off with paper and don't seal and glaze the surface of the stone, which would prevent abrasion. Start at the tip of the knife and apply strong pressure down and forward so that the whole side of the blade is in contact with the stone. Move back and forth, applying pressure. Keep the angle constant. Repeat on the other side. As the knife gets sharper and thinner at the end, go to a finer stone. When you are through clean your knife. Keep it sharp with a steel.