Criteria to make a good knife.
Let's see how the blade should be designed to cut well and can be sharpened easily.
To qualify it as a "good knife" is important to have the following qualities: good steel, good heat treatment, structure and appropriate edge angle. All must be present.
Besides the good steel and good heat treatment it is important that the blade structure including: the type of rebate, thickness and angles.
These details will determine that the knife will cut well, for a long time and let his sharpen easily.
Almost every beginner makes the knife blades with convex sections (Figure 1). It is a primitive criteria leaf design. It is very easy to make and very low cost, more similar to a machete (for a machete, you do not need a fine cut), it is only useful for chopping and axing branches or something.
Another very common type of construction is shown in Figure 2, which are unsuccessful knives simply because they do not cut.
Right angles are for a chisel, not a knife to cut the things we want to cut with a knife.
Often you will find a blade is made from a flat-parallel small plates, a rebate at an angle of approx. 25º and a bevel cutting edge of 55-60º, even up to 70º in some cases.
You should be reject the acquisition of a knife of these characteristics... it is useless.
Another widespread type of blade is made in a flat-parallel small plates with a small concavity as shown in Figure 3.
When it is new (see position A) it will cut relatively well until the wear and tear from use and the resharpening transform it to position B, where we find a piece similar to the case of Figure 2 with a cutting angle excessive for a knife blade.
So here we are eliminating many grams of useless steel.
Creole blades with section illustrated in Figure 4 have good performance at the beginning (position A), we use a section something thicker at the cutting edge (position B) which is going to be difficult for resharpening because it increases the worn surface, and so requires "lowering" the blade.