Sharpening steels. Types and purposes

When we talk about knife sharpening with professional chefs and butchers, one of the things that first comes to mind is knife sharpening steels. It is interesting that this tool is so deeply rooted in the tradition of those who work with a knife in their hands all day long. We mention these two professions in particular because depending in which sector one works, sharpening steels have different advantages and uses.

Considering that the main virtue of a knife is its edge, it’s not surprising that these professionals have tried to keep their knives in good condition. To do their job well, they need to cut easily and precisely. It’s easy to understand then, that sharpening steels which are comfortable and require minimal maintenance are so popular among professionals and amateurs.

However, what few people realize is that not all sharpening steels are the same, nor do they have the same purpose, nor is one tool always the best choice for sharpening. Here we introduce 3 main types of sharpening steels with different uses and purposes: Diamond, Ceramic / Titanium and Grooved steel.

• Diamond: The main purpose of this tool is to sharpen the knife. Because it is made from diamonds, this abrasive surface is able to “eat” or file away a large amount of steel from the blade with every stroke.
• Ceramic and Titanium: We can differentiate these by 2 types: those that can sharpen by removing material from the blade of the knife and those that can only set the edge. To keep things simple, both ceramic and titanium would be placed at an intermediate level in regards to quality.
• Steel: Sharpening steels are usually made with a grooved steel, that neither sharpen nor set the edge, but are used to straighten the edge after several uses.

What does straightening the edge mean?

The edge of a recently sharpened knife, rather than being triangular, has a shape more like that of the edge of a sheet of aluminum foil (the kind we use in the kitchen). If we look through a microscope, the edge is a sheet of metal that is so thin that, although it cannot be seen with the naked eye, it bends from one side to the other. A new sheet of aluminum foil has a straight edge, but if you start to slide your finger along the edge, exerting pressure, it tends to bend a little to each side. At the end, instead of a straight line, we have a wavy edge. The same thing happens with the edge of a sharp knife. In this situation we have not removed material from the knife as the amount of steel is the same. Instead, it has only been displaced. That is why the knife doesn’t cut exactly as those that have just been sharpened.

The stroke of a grooved sharpening steel has a similar effect as running your fingers along the edge of aluminum foil to straighten out the waves that have formed. We move all the waves to one side so that they are straight again. The edge of a knife is so thin that it is very resistant to dense materials, more so if it is makes contact with a piece of cartilage, a fish-bone or, although it should be avoided, a bone.

After several strokes with the grooved sharpening steel the knife will cut again better than before. However, the trick is that the knife should be previously sharpened, and all we have done is straighten the wavy edge. Had the blade been blunt or dull, little progress would have been made with the sharpener concerning the edge of the blade. This is because the sharpener hasn’t much capacity to remove that metal from the blade, only displace it.

But what is the difference between a dull edge and a twisted or wavy edge?

The difference is wear. When the edge is wavy, the amount of steel on the blade is the same, but when a blade is dull, it has lost steel. Knives become dull when the edge gets rounded due to wear and friction when cutting.

The cutting capacity of a knife is based on a simple physical principle: the pressure is equal to the force divided by the surface. Knives cut by pressure, splitting the material on each side of the blade. If the knife ends in a thin edge and is topped by a thin border, it will cut much easier than a blunt edge (thick or rounded).

So what then is the problem with the sharpening steels that really sharpen? At the end of the day, if they can remove steel from the knife shouldn’t they be considered a solution when the knife is dull?

Actually, there are unique uses to consider when using honing rods: The angle of sharpening and of course the pressure and the geometry of both the sharpening steel and the knife.

There is a sniper slogan that says precision is equal to consistency. This means that if you do everything always the same, you will always get the same result. just as it is important for a sniper to make an accurate shot a thousand meters away, it is also important to create the perfect blade at the absolute edge of the knife.

A sharpening steel, unlike a sharpening stone, has a small circular surface through which the blade slides. The rod also is held in the air with one hand (unless it rests vertically on a table, which is another less common way to use it) while with the other the knife is passed over it.

Throughout the sharpening process, neither the angle of the knife against the blade nor the pressure against the abrasive surface is constant. Furthermore, the passes are not uniform either. This,undoubtedly, is the biggest problem presented by these tools. Quality cutting cannot be achieved without a precise angle. Therefore a system that can keep a constant and precise angle is needed, or the sharpening steel fails its purpose.

With a whet stone we have a large flat surface, firmly resting on a table, on which we hold the knife with both hands. Because two hands are used to pass the knife across the stone, it is much easier to control the pressure. The angle is easier to keep because the stone is wide, flat and firm. The strokes are more uniform because both hands are sustaining the knife. We can feel what we do with it and how we move it. Because of its shape and its technique, sharpening steels don’t allow this kind of control.

Does that mean that sharpening steels are not good?

Not at all. There are two cases in which they are useful: for butchers, they are convenient for usual maintenance, and for chefs, as an emergency solution.

Butcher knives are battered through-out the day and come in contact with bones frequently, so the sharpening steel can be an element to keep the edge sharp throughout the day. Most Butchers even use their sharpening steels before every knife use, as a ritual.

In this case the sharpening steel can keep the knife performance despite wear. However, there are better alternatives. A diamond plate can be difficult at first but once you know the basic technique, you can get very sharp edges in the same amount of time as with the sharpening steel.

For butchers, whether they use the sharpening steel or the diamond plate, there is no excuse not to sharpen their knives with a whetstone at the end of the day, leaving them in perfect condition for the next day.

In the case of chefs, sometimes the knife falls, or it is used against fishbones or bones and the knife gets nicked. In these cases, we can use the diamond sharpening steel to quickly obtain a temporary edge to work with again, and then use the ceramic tool to soften the “serrated” edge, that may have been created and thusimprove the cut. I emphasize the temporary edge concept, since it is not a sharp edge with an accurate angle or a good finish. At the end of the day, that knife should be sharpened with a whetstone to recover the geometry of the blade and the sharpness of the lost edge. Resharpening it with a sharpening steel is no excuse not to restore it on stones afterwards.

In the previous case, instead of a sharpening steels, a diamond plate could also have been used. Diamond plates only need a few drops of water to work, they hardly take up space and can be used, cleaned and dried in a few minutes. Another even simpler alternative would be to have spare knives and leave the damaged pieces to restore later with stones.

As a final point, if you have to use the sharpening steel often so that your knife cuts well, throw your knife away and get a new one! This is a sign that at some point the heat-treatment has been damaged and the knife has become soft, usually when an questionable person sharpening your knives uses an electric machine and overheats the blade carelessly.

Reheating the blade of a knife beyond that which is necessary produces an over-heated surface (the steel heats up very quickly and cools very quickly), increasing the hardness on the outer layers and making the blade brittle and therefore producing an annealing in the inner layers (heats up more slowly and cools more slowly). This softens the steel underneath. To return the knife to a functional state, it is necessary to put it through all of the steps of the thermal treatment—a job that can only be done by an artisan who has the tools, the knowledge, and who is also familiar with your knife’s type of steel. It makes much more sense to buy a new knife.

And the above is one more reason to learn how to sharpen your own knives. The edge of your knife will always be in good condition, and the knife will last a lifetime.