Monday, December 3, 2012

Sharpening a kitchen knife with waterstones

Years ago, as a student of metallurgy, I was given this piece of advise by a steel plant manager: “If you can make a good steel, you can make a lot of money”. I never ended up making steel, turning to semiconductors instead, but I remember this message every time I look at kitchen knives.  I have bought several kitchen knives in the past 20 years, but the ones that have been able to stand the test of time have always been the priciest.  True to the plant manager’s advise, in steel you get what you pay for.

If steel kitchen knives are not sharpened properly, they are useless.  There are plenty of gadgets around but I have found none satisfactory.  The method I use was taught to me by a patient Japanese knifemaker on Kappanbashi Street in Tokyo—an entire street dedicated to the sale of kitchenware. It works very well.  Here is what I do.

Get yourself a couple of Japanese waterstones.  One with a grit of about 1000 and another with a rating of about 4000-6000.  There are natural waterstones available but these are expensive and geared towards loaded purists.  I buy artificial waterstones which work well, cost between $40-45, and are available on Amazon or any woodworking store. Soak the waterstones in water for at least a few minutes before you sharpen the knives and then make sure the surface is wet during sharpening.  

Hold the the knife on the 1000 grit waterstone with the front index finger holding it in place in the manner shown in the figure above.  The cutting edge of the blade should be against the waterstone pointing away from you and the blade should subtend an angle equivalent to putting two coins underneath the trailing edge of the knife. I do not actually put coins, but I like to think of this in Gedanken mode and simply eyeball the height. Just try to keep the subtended angle as constant as you can keep—and go by feel.

The waterstone is typically 2 inches wide and so this is the length of blade that it will sharpen at a time.  Divide the knife mentally into 4 or 5 sections of 2 inches-- each section will need to be sharpened separately. Start from the section closest to the base of the knife. Firmly and slowly move forward and backward for about 10 cycles, holding the edge down with the right index finger and steering with the left hand as shown in the figure above. This should take about 10-15 seconds.  The index finger should hold the blade at a steady angle.  Firmness and uniform motion rather than pressure is key.  The sharpening act occurs mostly on the push stroke and after a few strokes a slurry of grit particles will form.  It is this slurry that wears against the blade, sharpening it.

Now flip the knife so that the cutting edge faces you, and this time hold the knife and the angle in place with the thumb (see figure above).  Go back and forth again this time for about 7-8 cycles.  Now the major sharpening action occurs on the pull stroke. 

Repeat this process for each of the 4-5 sections of the blade, working your way from the base of the knife to the tip, till the entire blade has been sharpened.  Then go through this entire process one more time.  It is a lot quicker than it reads.

Try to slice a newspaper edge with the knife.  It ought to slice through cleanly.  If the edge is really sharp, you can also shave the hair off of your arm, but I am not a hirsute person and I don't need this depilation.  The thinking man cuts a newspaper.  It the knife does not cut, it needs some more sharpening, so go over the process again.

After the 1000 grit sharpening, go over the same process using the 4000 grit waterstone to give the edge a mirror finish.  I usually do just one round of 10 forward/8 backward strokes.

This process usually works.  If the knife has severe nicks then the blade needs to be sharpened on a coarser stone.  You could try a 400 grit waterstone or an oilstone.  When you buy the waterstones, it is helpful to by a cheap and coarse oilstone as well. 

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