Hoarded stones

The quality of natural stones vary widely even from within a single Aoto stone quarry. Natural defects include lines, cracks, too soft, too hard, or uneven texture. For example, if Aoto includes a sand, the edge is chipped during sharpening.
Before synthetic stones were available, carpenters were always looking for good Aoto at the hardware store. When they found a good one, they hoarded up all the good Aoto. Consistent high quality Aoto was very rare and very important for carpenter's work.

Started steady quality synthetic stones

The great carpenter Sadao Nomura led the construction for the “Hall of worship” within Meiji Shrine and the Noh stage within Shotou Kanze. He had many, many wooden tools. For example, he had 600 individual chisels for himself. His sharpening skills were awesome. He always took care of his precious tools so they’d be ready to use. He had some treasured good quality Aoto too.
But in 1970, the synthetic stone "KING deluxe #1000" was released. After trying the synthetic stone Sadao threw away all of his Aoto stones into the garbage box. He had spent so much money for his Aoto, but in the end its value was only as good as its performance in sharpening.

Various kinds of synthetic stones are released

I agree with Sadao’s way, because we are a knife making company. The savings associated with using synthetic stones allows us to push our costs down. The KING deluxe #1000 stone has better shaping power, keeps flat hardness, and gives a more orderly polished surface than Aoto.
Following the KING deluxe some years later the "KING hyper #1000" was released. The hyper (hard type) was much better than the deluxe.

Rating and reaching ultimate stones

We are evaluating these new stones, because we need good quality stone for making good knives. KING deluxe was rated a 5 out of 10. KING hyper was rated a 6 out of 10. I used many vitrify style #1000 stones. They were sometimes too soft, i.e. they had good hardness but didn't have shaping power. Or they had good shaping power but the sharpened surface was too rough like when using #800.
Our ultimate stone AI#1000 is made by MG style. The rating is the maximum 10 out of 10. (We have much experience and research data. You can see the rating of your stones, just ASK US!)

Synthetic stones have surpassed natural stones

There were great natural stones of coarse, and medium fine. Aizu, Numata, Ikarashi, Amakusa, Binsui, Tsushima, Jokyoji, Iyoto, Omura and Aoto were famous brands. However, the consistent quality and availability of synthetic stones in rough, medium fine, and fine grits has allowed them to surpass the performance of natural stones. Not to mention, many of natural stone mines are closed except for Amakusa.
Now, I only recommend the use of natural stone in fine grit. You can get miracle results with them. Please see at the natural stone pages!