Thread: How hard is hard, and how fine is fine??

Originally Posted by mainaman

For me hardness is related to how tight the bonding of the grit is , polishing stone should not release grit while honing on it.
Prepolishers are softer and more likely to release grit.

Alex could you explain your rating system to us? You use 0-10 if I am not wrong?

I agree with Stefan here. This explanation makes sense to me. I know I'm late to the party, but the hardness scale is subjective, assigned by the Vendor.
As far as I know, there is no bureau of weights and measures....Ha...!

Stefan


About 8 years ago when I first started selling Japanese natural stones I was carrying an inventory of about 75 stones which were all Old/New stock. My purchase funded an addition to the house for the little old man in Japan I bought my stock from.


I was sort of out there alone with these stones, So-san spent more time surfing than selling, and I did not know that much altogether. This was the Shapton 30k era. I saw a need for challenging Shapton, and no one, including So-san was willing to talk grit sizes or to speculate as to the grit particles of the stones. All anyone would say was it is fine, or really fine or super fine, or in So-sans case "my father does not like to talk about such things", etc. or very slow or slow or fast or very fast. I wanted to open up the market to fellows and professionals who were already using the finest handmade Japanese laminated tool and knife blades but were sharpening them with synthetic stones, really wasting the intentions of the blacksmiths.


It wasn't too long before I stepped off the deep end when I threw the figures "the grit can break down into the 30-40,000 range" for my best stones and about that time I invented a photographic system of observing the slurry to determine how soft a stone reacted under a blade and how jealous the stone was to cough up slurry. It did not matter if a knife or plane blade just so the system was consistant with the tester. I remember reading on this forum after a year or so, and on the knife forums also about that guy claiming his stones are in 30k to 40k range and how his stones are way too expensive.


Anyhow my scale of 1-10 turned out to be top heavy because I found that any stone below a 7 was too soft and useless for tools so as a consequence all my results were in the 8-10 range. Sort of like with the 1-5 system the 1-3 levels are too soft for honing so why include them except to discuss nagura. Here is an example of the way I designed my system. This was before Nakaoka-san (aka 330Mate) invented the simpler straightforward 1-5Lv system which Metal Master picked it up and then others like Maxium here and most everyone else now.

type in, thejapanblade.com/ and add, hard72.htm

It was about 5 years of selling stones before I was contacted by any razor users, you Stefan were one of the first, for stones for razor honing. At that time I only had large tool size stones and I was selling to knife and tool users all around the world, I had one amateur sushi chef in NY buy 5 stones within two weeks for $11,000 all overnight FEDX.

As it turns out the type of stones being touted right now as finishers were always regarded as too hard for tools until the idea of a Diamond Nagura was introduced by Peter Cowick, a sharpening sevant from back east. The DN really opened up a lot of doors for very hard stones which So-san would, until then, only recommend to be used by the most experienced sharpeners. Some of these were the finest stones and they were the most difficult to use and to hard sell.

I know that Iwasaki published a guide on how to sharpen razors using a progressive nagura sequence, and this is the traditional way. In Japan still even now only the avent garde will use a DN to raise a slurry, but this is changing in part because true nagura is getting expensive and hard to find in the finest grits. Although there was a line a number of years ago of very hard asagi Nakayama Stones I believe created by Hatanaka-san and tailored to Iwasaki's specifications, in the past super hard stones were not necessarily the first choice for professionals, it was always about cutting strength, speed. Speed gets the job done faster and in Japan one of the signs of a professional is to get the job done fast, correct is assumed, but fast is something to achive. And I was reminded of this when it was either Jim or Dr. Naka asked to see Iwasaki-sans razor hones on a post here, and the first one he pulled out was a lovely large kiita stone. Speed in important and this is why in my 1-10 Hard system I made a special column and noted the amount of black iron and steel particles within the slurry, the direct result of cutting as opposed to burnishing or what is being called polishing.

My Hard Tests were a crude way to try to create an objective way that sharpeners could discuss the attributes of a given stone. Obviously it was not a very successful method because over all these years no one ever contacted me to say that they had also repeated my test, and lets talk about it. Also the 1-10 scale is a bygone, I am now using the Lv1-5 test. Alx