There are several common ways to test sharpness:
- The fingernail test: will the edge grip the nail or will the edge just slide on off?
- Hair shaving: can you shave the hair off your arm?
- Paper cutting: how easily will the edge slice or push through thin paper?
- The 3-finger test: gauging the grabbiness of edge with just the fingerprints.
But what is “sharp”? How do you measure sharpness? Is there a sharpness scale or standard? Why yes… yes there is.
The Brubacher Edge Sharpness Scale (BESS) is what I use to quantify the sharpness of a cutting edge. BESS is administered by BESS Universal (www.bessu.org) which is a not for profit organization. To get a BESS reading on your cutting tool’s sharpness, I use the Edge On Up Professional. It simply measures the force required to cut a BESS certified filament. This gives us a very good idea of how sharp the tool is.
Now, with that said, there are factors which can skew the results one way or another.
- Example #1: The tool is not as sharp as measured.
I have found that toothy edges will often sever the filament with greater ease than blades with edges sharpened to a mirror polish. It’s not a huge difference on the scale, but it is noticeable. The issue is that this does not fully represent the real world applications.
Different steels have different compositions. Some steels are carbide heavy, which means that they have very hard “teeth” at a microscopic level. These steels are often harder to sharpen and they are more rust resistant. Others are made from purer, high-carbon, steels. Such steels are highly valued by chefs and purists for their ability to get sharper but they require far more maintenance to prevent rust and to keep sharp. Chefs and hunters prefer the high-carbon steels because they slice meat easier and they do so in a way that causes less cellular damage. Yeah, I know that sounds crazy, but it is true. Some knives rip through the meat and others slice. And yes, we’re talking about something that is happening at a microscopic level. And that is why a toothier edge can often show up as sharper than a less toothy edge on the BESS scale.
- Example #2: The tool is sharper than measured.
I sharpened a couple of straight razors for a client. Both razors were ready to shave when I returned them to this gentleman. They were able to top hairs (cut hairs midway up without). He was really happy with the results and the shave he was getting. But one of the straight razors got dull on him faster than he expected, despite him stropping them. I offered to check it out. I honed it back to razor sharp and then put it on my tester. It took over 1000 grams (that’s approximately 2.2 lbs to us Americans) for it to sever the filament. My razor was taking 70-75 grams. When I inspected the customer’s damascus blade, I found that even though it could slice through hair, the edge rolled hard where it was in contact with the BESS filament. The customer’s damascus steel straight razor was using a steel that was not sufficiently hardened. So no matter how sharp it gets, it will not keep that edge for as long as a properly hardened steel.
So, as you can see, sharpness is affected by several factors, particularly blade geometry and the qualities of the blade steel (hardness & carbides – amount and size). Different blades have different purposes. Most people don’t need an axe blade to be as sharp as a knife blade. And some knife blades need to have different geometries (type of bevel, edge angle) for different applications. But we still need a way to to measure whether something is sharp or not and understand what that measurement means. And that is why we have the BESS system.
I measure the sharpness of every knife before it goes out. It has to meet my standard before I say it’s ready. I hunt and cook… a lot… and I shave with a straight razor. I go camping and my camp knives need to have a balance of sharpness and edge retention. Every application is different, but each will have to meet my standard. I invite all of my customers to tell me what your needs are. If you want your axe to be able to shave arm hairs, then so be it. Just let me know. And if you want to know the BESS rating on your tool’s edge, please feel free to request it.