Surface finish on a cutting edge

Graphic with relation of edge thickness and width of sharpening bevel asymmetric edge

Edge Finishing

The finishing of the cutting edge has an impact on measured sharpness as well as the cutting feeling.

Cutting Feeling

If the edge has a smoother finish, it will produce less friction and glide through food more easily, thus producing a smoother cutting feeling.

Sharpness

There are lively discussions in different internet forums which edges are sharper, a very fine edge with mirror polish or a coarser, toothier one. Also, the cutting technique plays a role. For push cutting, the finest edge will produce the best results. For cutting in a slicing motion, some say that a somewhat toothier edge (but not really coarse) will work better.

There are different ways to finish (sharpen) the edge in mass production:

Dry finishing

This is the most common, most inexpensive and fastest way of sharpening, and how the edge of Western knives is produced. The blade is first sharpened on a belt, and then deburred/refined on a leather wheel.

One disadvantage is that the grit of the belt will generate a coarser finish and subsequently not the smoothest cutting feeling.

Another disadvantage is that if too much heat produced during material removal (visualized by flying sparks), it may overheat the cutting edge, change the material structure and cause chipping and corrosion.

Wet finishing

This is the common way of sharpening Japanese knives. The blades are first finished on rotating (water cooled) whetstones and then finished/deburred on a leather wheel. This method is often called “Honbazuke”, which literally translated means “true cutting edge”.

The advantage is that the cutting edge will have a smooth finish and thus be sharper. Also, due to the blade being cooled by water during sharpening, there is no risk of the edge becoming overheated.

The disadvantage is that it’s a more time-consuming and thus more expensive way of sharpening.

Number of production steps

The number of production steps necessary to put a cutting edge on a blade depends on the following:

Thickness of the blade on the edge prior to sharpening
Targeted edge angle
Targeted smoothness of the edge

In general, the more material needs to be removed from the edge to sharpen the knife and the smoother the surface should be, the more time and production steps are needed.

If the edge is too thick prior to sharpening, material would need to be removed in 2 steps, pre-sharpening on a belt or stone with a lower grit and fine-sharpening on a higher grit, before the final step of deburring/refining on a leather wheel.

In case the blade is very thin to begin with, one may immediately move to fine-sharpening on a high grit immediately and skip pre-sharpening.

Also, if the blade shows a wide bevel after the Frist sharpening step, more production steps may be needed for refining the surface finishing. If the bevel is small, this can be done in one step.

So the number of production steps in sharpening is not necessarily an indicator of quality of the sharpening process.

Width of sharpening bevel

Since the sharpening of a knife must be done at a wider angle than the one at which the blade is ground, putting a cutting edge on a knife will usually produce a bevel.

The width of the bevel will depend on blade thickness and edge angle, as illustrated in the below drawing.

The thicker the blade, the wider the bevel (see pic. A vs B). And the narrower the angle, the wider the bevel (compare edge on pic A and B on left side to edge on the right). So a wide bevel may hint to either a thick blade or a narrow edge angle. However, the best and sharpest knives are those with an acute angle, but without much of a visible bevel, since this shows that the blade is very thin on the edge.