Natural whetstones are superior to artificial whetstones for the purpose of beautifully finishing knives.
The beauty of knives is not only the brilliance of a mirror-like luster. The uneven sharpening of the fine particles of the natural whetstone diffusely reflects the light, giving the knife a dull shine.
The pattern drawn by this dull luster is called "kumori" and is appreciated as a beautiful finish unique to natural whetstones.