a Japanese sword specialist, and 4 and 5

4. Is there a certain style/school/period you like and why?
I enjoy each blade for its own merits including shinsakuto.
5. Let’s say we have a +500 years old blade (maybe unsigned) in our hand that seems to be preserved very well at first sight. How do we determine it’s origins and health? It may have been used in many battles and most likely had a lot of ‘facelifts’ through the years to keep it ‘nice looking’.
This is a complex subject that cannot be answered simply. We discuss this in depth in our book Facts and Fundamentals of Japanese Swords (Kodansha international), I would recommend further reading on it there.
As for determining its origins, one must look at the sugata (lit. shape, but also incorporates dynamics) to determine the period. Next, by looking at the folding pattern of the hada, in combination with the hues and textures of the jigane, one can determine where in Japan, or by which school the blade was produced. Then, finally, as one inspects the pattern and quality of the hamon, it is possible to determine the actual maker of the blade by the idiosyncrasies in his hamon application procedures. Like analyzing handwriting, the smith’s habits appear in the consistency of his hamon through the timing of his quench, and the activities that appear in the hamon through the way he applies the clay.
However, from a more pragmatic point of view, as the workmanship of blades is subjective, there is no 100% guarantee of a correct attribution to the maker of a blade that is unsigned, or has had the signature removed. The most that can really be gleaned from the blade is the school, or tradition. Any speculation beyond this is purely the appraiser’s opinion. Some opinions are more reliable than others, but unless you were there at the time of the forging of the blade, or the time of the signature removal, it is only an educated guess as to who the maker is. In the Koto period, smiths had many students, and the many students’ work is likely to be similar to the teachers’. It is also estimated that during the Koto era there were at least one or two smiths per village all over Japan, therefore increasing the chances of many unrecorded smiths, and the possibility that blades similar in workmanship to mainline smiths, or of unknown origins were made.
Today with the improved techniques of polishers, many polishers are able to hide most flaws, and the appearance of a blade can change radically from one polish to the next. The objective of a modern art polisher today is to recognize from which tradition, school or maker the blade is from, and bring out the correct shape and characteristics that correspond with that attribution. However, the nugui application alone can change the tone of a blade and help to hide umegane repairs and the like.
However, blades can only diminish with age; steel lost through battle damage or numerous polishings cannot be replaced. There is an old adage amongst polishers: “You can take it (steel) off, but you can’t put it back on.” This is to remind polishers to be conservative at all times when polishing blades. So, when looking at a blade it is helpful to know what a healthy example of a sword from the same period should look like. First, check the overall sugata, and compare it mentally to a healthy example. Then check for funbari in the area from the machi and a couple of inches above. If there is no funbari, this means that the blade may have been adjusted or shortened (okurimachi/suriage). Also check for nakago funbari. The area of the nakago that meets the machi should fan out. If it does not, this could mean that the nakago has been filed down just below the machi to accommodate wear to the cutting edge. Does the hamon run off? Does it have an original boshi? Are there patches of plain steel or different hada amongst the overall hada? These could be patches of core-steel coming through the skin-steel. These are all classic indications that a blade may be ‘tired’, or worn.
Want to buy a sword! Point I...