Originally Posted by
Gammaray
You are so right about the "mythical grit" ratings. We actually agree more than you may think. You continue to make my point with your comments in that above the 4,000 level grit level ratings get more uncertain and are estimated. The 0.5 micron CrO level is specified by most at around 30k. But your diamond pastes may say 50k. They are very inconsistent. What are we to believe?
One of the issues is that the original grit rating was based on AVERAGE particle size which could substantially vary. These were based on a few common substrates and were rarely higher than 400 grit. Extending the original grit standard above this is very difficult because it gives no consideration to hardness, particle shape, or effectiveness which vary with the substrate material. The new diamond pastes really have no grit equivalent due to these issues. A 0.50 micron diamond particle may be comprised of a variety of irregular crystal shapes with jagged edges corresponding to a wide range of effective grit levels, while the beauty of 0.50 micron CrO is a remarkably round, smoother crystalline shape with less pointed corners.
It is interesting that tanned leather may contain as much as 5% chromium compounds (also used in stainless steel), sulfates, salts, and other compounds capable of scratching carbon or stainless steel. This is why I estimate that the effective grit of leather is at MOST 90,000. Linen is not as predictable as there are so many varieties now, but depending on the processing method untreated, unpasted linen is most certainly LESS than leather unless it has something added. Of course regular readers of my posts already know that I use linen to clean my blade not to refine it. I believe untreated linen has a much HIGHER grit level than leather for the reasons stated. Of course we may all have opinions on this topic because like you I don't think there is a definitive answer to these questions. Thanks for your push back. It obviously made me think a bit more about this issue. :)