Not really. Most Japanese natural stones should not be soaked at all. The chosera stones need no more than a few minutes and should never be soaked for more than 1 hour due to the binder (says so on the stone
).
There is NOT a perfect time delimited countdown that can guarantee the perfect wetting. Only Chosera 400/600 need to be "soaked" at the point of not releasing any longer any bubble (normally 2minutes in tap water) after which putting a veil of water sparingly will do. 5k Chosera is very thirsty and 10k is but less than 5k, when we would expect quite the opposite: I don't soak Chosera excluded the above mentioned.
Coming to
Natural Japanese I would add some more literature as you've correctly said that not all of them require soaking (yet I didn't mean happily floating in the water for a couple of hours).
Origin and Cut: The names of the stones generally come from the mountain where they were quarried. Here are some examples of names from Kyoto and its surrounding region:
Western mountains: Ohira, Shinden, Mizukihara
Central mountain: Atago
Eastern mountains: Nakayama, Ozuku, Kizuyama, Okudo, Shoubu, Narutaki
Currently nearly all quarries are closed. But there still exists a lot of raw stone material mined in the past waiting for being cut to appropriate sizes.
The stones are cut horizontally, so that the layers of sediment are parallel to the stones face in order to present a consistent grit size and quality. This can be compared to flitch-sawn wood.
The
proper watering time serves to stabilize the structure of the stone to allow consistent results. It is important to remember that these are natural stones, every one is different, and so each has a different need for water. Harder stones, for instance, need more time in the water than softer ones.
But, recognized and respected experts in Japan also say that regularly-used natural stones can be left permanently in the water. They base this advice on the idea that, contrary to the various kinds of artificial stones which can be damaged if left in the water too long, natural stones can withstand this treatment in that they are in principle stones that were formed under water (sedimentary stones).
I disagree.
Natural sharpening stones are normally composed of about 2/3 SiO2 (Silicon-dioxide), which provides the sharpening grit, and about 1/3 KAl2AlSi3O10(OH)2 (Sericite, finely rippled Muskovite) which serves as a binding material. The stones were formed about 70 million years ago. As they were formed from sediment laid under water, one would think they would be stable when wet. But after the stones have been quarried and cut to size this can change, as the binding material, which is at least in part water soluable, can dissolve over time and the abrasive particles can flake off unevenly. This decomposition process normally takes place over many years, and so if the stones are in use every day, it doesnt matter much at all. But for most people today, to respect the investment in the stones and their quality and rarity, it is best to store them dry to avoid any possible damage and exposition to heating/cooling plants.
[Edit]
The most important lesson had been learned the hard way.
One day last year I broke my Chosera 600 because I took it out from resting at 20°C and put under very cold water (10°C or alike). How much water it is a matter of experience, but the least Thermal shock as possible it should have been just plain common sense. Me dumb
