Originally Posted by
Euclid440
As Robin says at about 7.05 in the video.
“The nature of this is completely contrarian to normal stoning like mould polishing where you want the abrasive to be aggressive. This is a completely different stone.”
The goal of these stones is to polish a flat surface. Dead flat for honing is not that important, you want stones that will cut a progressively finer smoother edge and very few razors are flat. You are polishing a surface that is 1-2mm wide. The goal of polishing a bevel is to make a straight edge with smaller serrations, not a shiny bevel. But the only way to hone the edge is to polish the bevel. A shiny flat bevel is the by-product of a straight finely hone razor edge, not the goal.
You can polish a bevel with any good metal polish that is mirror finished, but the grit in metal polish (usually Aluminum Oxide) is large and aggressive and will leave a serrated edge, unsuitable for shaving, great for knife, and tool edges though.
With deburring stones, (320 grit India stones) you are polishing much larger surfaces, with large grit that has been flattened.
Robin does not show you what the surface looks like under magnification, because it is not important to his objective, he is after flat, not polish. To the naked eye a good 8k bevel looks like a mirror finish, under 60-100 x magnification you see all the imperfections and what they do to the edge of the work piece, not all 8k’s are equal.
As said, all he is doing is burnishing a stone face. The same thing happens with old sandpaper, the space between the grit fills with swarf and the grit flattens out. Allowing or forcing the paper and grit to make a smoother surface. The grit is still the same grit in width, just not in height, and will cut stria the width of the grit. In this case you are cutting 320 grit stria.
Robin also states “There are no other methods to do it that work. You can’t lap them. You need a good surface grinder and diamond wheel.” (You need to cut the tops of the grit uniformly).
You will also need 2 identical stones to maintain flatness, after ever few laps you must rub the two stone together to flatten the swarf between the grit in the stone.
Probably a more practical video of Robin’s is his surfacing lapping plates. But here again, dead flat is not critical for honing razors. Robin is a pretty smart guy with some great videos on his channel.
Technique trumps stone grit and flatness every time. India stones are great for repair work and great knife and tool stones.