The difference between natural and artificial grinding stone work
No matter which way you sharpen with a faux stone, scratches on hard and softer steel will be basically the same.
Artificial whetstones can be sharpened relatively quickly, but they are too abrasive and create grooves that are difficult to remove, making it difficult to get a long-lasting cutting edge. Natural whetstones, on the other hand, have a low abrasive power, so they will take quite a long time to sharpen, but they are less likely to weaken the blade and are easier to finish to a high standard. In addition, since the soft parts of the steel material are ground away and the hard particles (carbides) remain on the surface, the blade lasts and cuts for a long time.
In other words, natural whetstones are less likely to warp or split the steel, resulting in easier sharpening of the cutting edge, better sharpness between the soft and steel line (san mai) and longer retention of an aggressive cut compared to man-made whetstones.
The difference in blade appearance after finishing between natural and artificial stone
Artificial grinding stones evenly polish both steel and soft iron using a powerful abrasive, so there is little difference in their shine or reflection on objects. Also, because the abrasive particles are sharp, scratches on base metals and steel often cannot be removed. On the other hand, natural grinding stones have different grain sizes and compositions, so steel and soft metal react differently. Differences are easily seen in terms of polishing speed, scratch formation and gloss.
The difference in grit numbers (#) between natural and artificial grinding stone
Artificial grindstones range in size from 40 to tens of thousands, but numbers vary by manufacturer, and some can leave deep scratches due to mixed abrasives. On the other hand, natural finishing stones are said to have a grain size of #7000 to #10000, but after sharpening, the abrasive grains gradually break down and become finer, making it easier to achieve a uniform sharpening surface. In this case, the result cannot be expressed simply as a number.
Corrosion resistance difference between natural and artificial whetstone
When comparing a natural and an artificial grinding stone of almost the same grain, the natural finish is more resistant to corrosion. Steel treated with artificial sharpening stones tends to rust, even if their grain size is 1.5-2 times larger than natural ones.