It’s easier to keep your knife sharp than it is to sharpen your knife – Howard B. Schechter,1990
The Age of Metal came about 5,000 years ago and brought with it the need to sharpen metal tools. In the Stone Age, one simply flaked off a new edge from a piece of flint or obsidian and threw it away when it was dull. It was soon noticed that rocks from certain locales sharpened metal tools better than other rocks. Whetstones were added to the growing economic system of trade that spread along the trade routes to Turkey, Asia, Europe, and the Americas. Coticules from Belgium, Eidsborgs from Norway, Tam O’Shanters from Scotland, Arkansas’s from the U.S. and on and on. We’ve been shipping rocks around ever since!
There are so many variables to be mastered when attempting to achieve the perfect edge! The beginner can get a reasonable edge fairly quickly by following a few simple guidelines and can then spend a lifetime mastering the craft of “whetting”.
The basic procedure is to rub the steel on the stone using a consistent angle between the blade and the stone. And there’s the rub (so to speak…)! Let’s answer a few frequently asked questions.
What stone should I use to sharpen and hone my tools?
Depending on what you’re sharpening and how dull it is, you may need several stones of different grades. If a tool is really dull, the most efficient way to get it sharp is to progress from a Coarse stone to a Medium stone to a Fine stone and then a Finishing stone.
Should I use oil or water or nothing when I hone?
The answer to this depends on what kind of stone you’re using. A Belgian Yellow Coticule or Blue stone require only water to make the abrasive slurry on top of the stone. The abrasive slurry is what is sharpening the tool. A DMT stone is wetted down with a mild soapy solution. An Arkansas stone is usually used dry but one can use oil on them.
A DMT Diamond Stone should be used with a soapy solution of water. I use 4 or 5 drops of liquid dish detergent to 4 oz. of water and that is what is recommended by the brilliant folks who make these stones. One could also use the DMT stones dry.
A Norton Waterstone should be soaked in plain water for about 5 minutes before it is used. Oil is not recommended for waterstones.
What is a strop?
A strop is a piece of leather, usually oak or vegetable tanned, either hung from a peg or mounted flat on a paddle. Stropping is always done away from the edge. Honing is done towards the edge. Stropping and honing are fundamentally different processes. The only treatment I give to my strops is an occasional dressing of Fromm’s Strop Dressing. I don’t use any kind of abrasive paste on my strops.
Do I need to use a strop?
If you are honing a straight razor, you need to use a leather strop. The leather puts a final finish on the edge of the razor by drawing the razor edge away from the edge. Practice this using a leather belt or a piece of leather glued to a piece of wood. Use only oak tanned or vegetable tanned leather. You do not need to dress the strop with anything, just use the naked leather. Knives or wood cutting tools may be stropped but that’s personal preference.
How do I know what is happening to the edge when I’m honing?
The best practice I know of is to use magnification when working on an edge. Use a jeweler’s loupe, a magnifying glass, a microscope or anything that will let you look very closely at the detail of the edge of the tool. Use good light to catch the reflection of the edge and look at the scratches along it. You’ll be amazed at what you see. Check the toe, heel, and center of the edge on both sides and you will see differences that will need different treatments. This will even be true for newly manufactured razors, knives, tools, etc. which have what we call a “factory edge”.
How do I test the edge to know if it’s ready?
This question is the subject of much debate and the unfortunate truth is that there are no standard tests which will tell you when the edge is ready. Bladesmiths will often cut a piece of paper held in one hand. Straight razor users will hang a hair strand and hold the razor up to the hair and touch it. If it pops! in two, the razor is ready. This is the Hanging Hair Test (HHT) and it is not a standardized test due to variations in hair strands. Having curly hair, I can’t use this test. There is also the test of cutting off a piece of thumbnail. This test originated with the ancient Jewish “schochets” who cut the throats of animals in the production of kosher meat. It’s an excellent test for a sharp blade.
The best way I know to test any tool for sharp readiness is to cut what the tool was designed to cut. A sharp plane iron in the hands of a woodworker will shave wood so thin it will be translucent. A sharp straight razor will give you the closest shave of your life. My shaves give me a day and a half of clean shaven face. You will know if the edge is ready to cut as it won’t drag, dig, skip, or otherwise act improperly.
What about the burr?
During the sharpening process, the metal at the edge will roll backwards from the edge. This is the “burr”. You will read about the burr on the edge of the blade as a means of testing the blade’s readiness for advancing to the next step in the sharpening process. The formation of the burr occurs on most steels, most edges, most edge geometries, and through most honing processes. Notice the use of the word “most”. It doesn’t always happen but it is something you have to be aware of when sharpening anything. You will know it has formed either by feeling it with your finger or fingernail or by actually seeing it. The burr needs to be removed.
My personal opinion about burrs is that I don’t like them. I have been making hunting and Bowie knives, machetes, drawknives, tools, etc. for over 25 years and go to extraordinary lengths to get an edge designed and executed to where it needs to be for a particular tool and use. I sharpen them and keep them sharp. Forming a burr that gets removed loses too much metal every time you hone. My tools get sharp without my getting a burr and I work with blades constantly whether I’m shaving with a straight razor, chopping wood, or cutting meat.
Having said all of that and knowing there are other opinions out there, it is worthwhile to read the study in the next section.
Photos of the Burr
Sharpening processes have been extensively studied in order to add to our understanding of what is actually occurring at the edge. An interesting study was conducted and reported on by Prof. Dr. John D. Verhoeven of the Dept. of Materials Science and Engineering at Iowa State University, Ames, Iowa, in 2004. This 55 page study is worth looking up as Prof. Verhoeven has included Scanning Electric Microphotographs (SEMs) of the edges of blades under very carefully controlled laboratory conditions. An SEM is worth a thousand words.
Factors Affecting the Ability of Blades to Take an Edge and Keep it
The ability to take an edge and keep it is the result of the type of alloy used and the hardening and tempering. Simple steels with few alloying elements rely solely on the formation of iron carbides for their hardness. Steels with more alloying elements such as vanadium, cobalt, manganese, chromium, tungsten, etc. require a more complicated hardening process at different heats for different amounts of time because the carbon forming the vanadium carbides, cobalt carbides, tungsten carbides, etc. form at different temperatures.
Hardening temperatures are usually in excess of 1000 deg. F and are often in the 1200 – 1400 degree range. The temperature has to be closely and accurately monitored so that the steel can be quenched to low temperatures ranging from room temperature to maybe 150 deg. F very quickly. This is what gets the bladesmith the optimal performance from any alloy. The phase change in the steel (at quenching) has to happen very quickly and often within seconds or it won’t work right. This is one explanation for a blade failing to perform.
Quenching liquids include water, various oils, air, or salt brine. A2 tool steel, for instance, is air-hardening and tends to warp less on cooling. 01 is an oil hardening tool steel. 1095 tool steel is best quenched in a salt brine.
Tempering temperatures range from 430 – 600 deg F and tempering is actually a softening process which also makes the metal tougher. Hardened steel that is not tempered is very brittle and not tough at all. Tempering should follow hardening fairly soon or the steel could ultimately end up not performing as expected. Tempering can be done in a toaster oven, a low temperature kiln, or in a forge – be it gas or coal.
Tempering can be done in a lead bath, as someone noted, as the temperature of molten lead is 600 deg. F. Hardening has to be done at much higher temperatures in an electric kiln, gas or coal forge, or even using a cherry tip on an oxy-acetylene torch rig (I’ve done this).
The end result of all this is an edge that can take an edge and keep sharp due to a variety of factors that interplay and include number of carbides present, size of carbides, grain size, zone of hardened steel along the edge, etc. It’s all quite complicated and people devote lifetimes to mastering the art of heat treating. At least one prominent heat treater in the knife industry says that you can do everything right and still not get the results you expect! It’s an art as well as a science.
So why do some blades fail to perform?
Alloy, heat treating, grinding (get a thin blade too hot while grinding and it will lose the heat treat), and type of grind. There are steels that don’t do as well in a hollow grind as they do in a more angular, beveled grind.
Nonsense You’ll Read on the Internet
Every once in awhile someone will say that the old stones are of higher quality than the new ones being mined today. I’ve tried to track down the source of this rumor in the hopes of finding some actual evidence. The search has been unsuccessful. The stone mined today is the same 400 million year old stone that was mined 100 years ago. For whatever reason, there seem to be those in every field who claim that “the old stuff” was far better than what we have today. They claim it’s true for blade steel, pollution being less on vintage cars, wood, the agrarian life, etc. This prosaic longing for what was rather than what is may be a sign of melancholy.
The following excerpt is from a book written by a Cornell University professor in 1908. I’m including it here as I found it so fascinating that once again, Koheles, author of Ecclesiastes, was correct when he said “There’s nothing new under the Sun”.
Students of honing will recognize much here and some ideas will be new to many recently engaged in the pursuit of the perfect edge. Gage used the best tools that could be had at the beginning of the 20th century – Belgian and Arkansas hones. Artificial diamonds had yet to be invented and so he had no diamond stones by which to lap the factory hones. How little has changed! We’re still not getting flat stones and have to lap them ourselves.
The most interesting tidbit, for me at least, is his method of removing microchips from the edge of the microtome. He holds the knife on edge on the stone and with only the weight of the knife drags it across the surface to take the whole edge to the same level. Then, after the edge is chip free he hones it and strops it using the Belgian coticule as the finishing hone.
The Microscope: An Introduction to Microscopic Methods and to Histology
By Simon Henry Gage, 10th edition, 1908, Comstock Publishing Company, Ithaca, New York.
p. 288, section 435
Sharpening Section Knives; Hones and Strops
Perhaps it should be taken for granted that any one would appreciate the impossibility of making good sections with a dull knife, but experience teaches the contrary. Students are prone to believe that with one of the elaborate automatic microtomes, good sections may be made with any kind of an edge on the knife. It is forgotten that the knife is the most important part, all the other mechanism is simply it’s servant.
For sharpening, select a fine, yellow Belgian hone, and a very fine Arkansas hone. As a rule, hones from the factory are not sufficiently plane. They may be flattened by rubbing them on a piece of plate glass covered with moderately fine emory or carborundum wet with water. Round the corners and edges of the hones on the plate glass or on a grindstone. In using the Belgian hone for sharpening knives, wet the surface well with a moderately thick solution of soap. With the Arkansas stone, use some thin oil – xylene or kerosene mixed with a little olive oil or machine oil.
Gage’s recommendation to use a thick soap solution on the coticule is an interesting one. Today, the Belgians recommend only water. – Howard
Honing. Before honing a section knife, make sure that the edge is smooth, that is that it is free of nicks. Test this by shaving off the surface of a block of paraffin. If nicks are
Interesting test! It’s quick and dirty and doesn’t require magnification. – Howard
present, the cut surface will show scratches. It is advisable also to look at the edge of the knife with a magnifier and with a low power (50 mm) objective. If nicks are present, remove them by drawing the edge along a very fine Arkansas hone.
We don’t know what grade of Arkansas stone Gage used but I have done this on a DMT1200 Extra Fine and a Shaption 1000 GlassStone. – Howard
A saw edge may be alright for rough cutting and for straight razors, but if one wishes to get sections 2 – 10 microns in thickness, a saw edge will not do. In removing the nicks one should of course bear on lightly. The weight of the knife is usually enough.
HA! Gage had higher standards of edge quality for the microtome than for a straight razor. He may have written this 100 years ago but we’ve got some pointers here from a fellow who knew Belgians and knew a . . . perfect edge. – Howard, 6/20/08