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GRIT TEST PROCEDURE
I developed this Grit Test Procedure as a home style scientific system in an attempt to photographically capture for comparative purposes, the scratch lines or scratch pattern left on a Japanese steel kanna blade by different sharpening stones. I designed this method so that almost anyone could replicate the method themselves with a minimal amount of cash output. The actual grit particle size of Japanese finishing stones, awase toishi, has been a topic of discussion that has been based primarily on the opinion of the owner in relation to how the stone feels, or how "sharp" the blade gets after using the stone in question. I am not suggesting that the owner of any stones in question does not have an excellent perception of the cutting qualities of their stones, but instead I have been simply looking for some way that 2 parties can have an intelligent conversation using visual aids.
I choose to use the Sharpton 30,000 grit Glass Stone, product number 50403, as a jumping off reference point because this is a stone that is readily available and at 30K it represents the finest grit particle normally used by woodworkers in a synthetic manmade stone formula. Conversely, the Bushnell Portascope I use is also available and can be purchased on the internet for as little as $24.00. It is similiar to what is called a Dissection Microscope where the specimen area has room to place a larger object and the illumination comes from above or the sides. My camera is an older Olympus with a optical zoom. I illuminate my subject from one side only with a simple halogen table lamp. Any lamp or camera will work as will any microscope that will allow the above requirements. The software I use in my computer is a 1999 version of Adobe Photoshop Delux, it came free with my Epson printer (long gone) and I have used this program in all of my computers since then.
The photos are based on a scale of 1 centimeter. For my purposes this is close enough and when magnified on a 25cm. wide computer screen it represents a magnification of about 25 times. The camera is set to the macro-zoom to get the close shots, and the photos are then reduced a small bit in the computer. My intentions are to compare the scratch patterns on a given blade, not to delve into the microscopic make up of the blades metal composition, so this power seems good enough for those purposes. The lack of resolution, depth of field and lack of focus from side to side is more than likely from the poor optics of the Portoscope. All of the equipment could be upgraded, but at what cost. For my money, this is working OK for now.
Originally the blade I was using was a 1940's-50's Ishido Teruhide Swedish Blue Steel 70mm kanna blade. I am now useing a 1950's Hitachi 70mm Super Blue Steel blade made using the VIM vacuum induction method. The blade is marked on the front HOJOJI, a historical reference, specifically to a Kyoto Buddhist temple, and sometimes poetically used by Osaka/Miki area blade makers, and on the back SHINKU meaning vacuum. I like this blade because the reference points I am using for scale in the soft iron jigane are deep and prominent and will hopefully appear through many sharpenings.
The light source I use is from the left side, and at a parallel to the blades cutting edge while being at a right angle to the scratch pattern left from the sharpening stone. The light may need to be adjusted by a degree or two in order to draw out the reflective brightness of the scratches but I use the same set up for each photo including the photo after using the Shapton stones.
I trust that the following photos will fill in any blanks I have not dealt with in this short description above. As you can see there is no mystery to these tests, and they are simple enough so that very little information can be falsified or manipulated. Any suggestions and comments will be greatly appreciated.
