GRIT TEST ON SUITA AWASEDO #13

The photo comparison tests for the grits 12,000 and 15,000 I used a vintage 1940's-50's Ishido Teruhide Swedish blue steel 70mm kanna blade. For the photos of the Shapton 30,000 and the Suita stone numbered above I have switched to a vintage 70mm super blue steel blade marked HOJOJI that is stamped SHINKU (vacuum) on the back with refers to the Hitachi Vacuum Induction Method.  I changed blades because the registration marks, in the form of black spots in the soft wrought iron that I used as my cameras target began to wear thin on the Ishido blade, and I found this Hojoji blade that had really deep spots that would work better. The sharpening qualities of the two blades is similar.

The progression from the courser synthetic stones through the finer synthetic stone in the images can be duplicated at any time with those or similar stones GO TO TEST PROCEDURE. If you follow the test procedure you can then use your own natural stone in the same procedure and compare to the synthetic grit pattern sample to determine your own estimated grit particle size of your natural stone. The enlargement of the photos in my test is about 25 times. 

In the photos below, the scratch marks left by the man-made synthetic stones look deep and long when compared to the scratches left by the natural stones. This appears to be typical of synthetic stones which are formulated go cut aggressively and fast. The hard cutting compounds, usually a proprietary ceramic or oxide of some form, do not break down into smaller particles as readily as the organic compounds do in the natural stones. The synthetic stones tend to leave the soft iron or jigane looking scarred under magnification and when viewed with the naked eye the hagane and jigane look equally shiny.

I do not have a scientific explanation for this phenomenon but only can suggest that as I see it, the scratches from the synthetic tend to transcend between the two metals as a full dimensional grit particle scratch, where as the natural stone particle looks like they may or might cleave or reduce in dimension in the transition from soft steel to hard. This may explain why the natural awase toishi tend to leave the finished blade with more contrast between the hard steel and the soft iron, polishing one metal to different degree than the other metal.

Another explanation may be as follows. I would suggest that in the photos below where you see the grit pattern scratched into the extreme cutting edge of the blade by Shapton 30K stone, those small finer scratches are probably more in line with those of a 30,000 grit particle profile. If that be the case then those shorter in length and finer scratches are indicating possibly that; the synthetic particles do break down somewhat, or that there is some burnishing effect occurring.

Another more logical explanation might be that in the proprietary formulation of the synthetic stone, the bonding agent may be bonding individual particles together in such a way that they are cutting the steel not as individual cutting particle agents but rather as a group of particles tenaciously bonded together and acting and cutting the steel and mimicking themselves as a singular larger grit particle. This is a phenomenon Leonard Lee describes with text and photographs in his excellent book The Complete Guide to Sharpening. If I may quote Mr. Lee in his reference to Hard Arkansas stones on page 31 & 32, "A further problem with the very tight nesting of the particles is that some of the bond lines are stronger than others and it is possible to get a large number of particles acting like a single particle." he further notes that, "I have found this anomaly only in Black Hard Arkansas, not in any other of the Arkansas stones." I will not further quote Mr. Lee without his permission but I would suggest anyone truly interested in the subject procure a copy of Mr. Lees' book as he goes on to elaborate further on this subject and others and the photos throughout the book are fantastic.