The question to ask is what is the objective in your heat treatment? Is it aesthetics, is it optimum blade property development, is it both?
If your sole goal is how striking the hamon can look than it parallels some damascus in many ways, in that there are those who don’t mind pure nickel and other things on the edge since the eye catching contrast is the main thing that quickens their pulse. If the number one priority for you is the shape and boldness of the hardening line, then you can vigorously pursue that aspect without letting optimum microstructures or other properties being a distraction. It really is crucial however that you are totally honest with your customers, but most importantly yourself, if this is the focus of your efforts.
If however the optimizing of microstructure along with the best properties for both edge holding and overall blade strength are your goals, then the intentional pursuit of the opposite in parts of your blade will naturally be a compromise of your ideas. In order to have a traditional hamon you will need to form ductile pearlite in the bulk of the blade; a phase that is the goal of proper heat treating to eliminate as much as possible. Martensite, the fully hardened form of steel, is indisputably the strongest phase possible, so blades with pearlite spines are not stronger, they are more ductile. Ductility simply means the blade will bend instead of breaking, but it will bend with perhaps five to eight times less force required to break a through hardened blade which possesses true strength.
You may, however, walk the middle ground where you are willing to compromise overall blade strength for a visually striking hamon, but still not wish to lose any desired properties at the edge. This is very possible but requires a very good handle on things, along with the highest level of honesty with yourself and others from the first two approaches. You need to have the clarity of thought and the self discipline to resist the temptation of playing with soaks and quenchants in order to bring out the boldest hamon when they could compromise the structures of the edge. It is in the failing of fully understanding this balancing act that hamons can be one of the biggest stumbling blocks in making blades that will live up to the claims of many custom knives. When one feels that water is the only way to get that eye popping hamon and they start under-soaking the steel in order to avoid the hazards of such a quench, they are short changing the optimum condition that steel could have achieved, even at the edge. Some will say that they get better results with eyeballing heat in a forge than using precisely controlled heating equipment, but what they really mean to say is that they get better looking hamons using that method since the optimizing of austenite solution is no longer a distraction. In yeat another area, if that funky shaped hamon can only be achieved by applying the clay in a manner that impinges too much on the full hardening of the edge, the same will naturally suffer. Likewise edge quenching will also present the same threat but on a greater level due to the greatly retarded cooling power of the oil on such a limited area of a very hot piece of steel. And the real challenge to self policing here is that one cannot tell how much fine pearlite is in the edge by looking at the hamon. The hamon only reflects the martensite and coarser pearlite boundary; you need to cross section the edge and find those nasty little fine pearlite colonies with a microscope, or compare the compromised edge performance with one of known optimum quality. And fractured grain examination can only tell you about the two different phases in such a blade, not very much at all about austenite grain size since the mechanisms of fracture are so different between the two. It is a common a tragic mistake made by many beginners in an Intro to Bladesmithing class to compare the coarse looking surface on the spine, the fine smoother looking surface on the edge and start to believe in some sort of edge packing or magic grain refinement. However the grain size will be the same for the entire blade as determined by the heat you applied, just pearlite fractures with more slip and shearing causing a rougher looking surface than the clean cleavage of martensite.
So the hamon may, or may not, be a great heat treatment, but it all depends on what you really want from you heat treatment and how much you are willing to objectively look at and study the results of your efforts.
But it sure looks good when done properly.
