to-ishi　砥石

KEY WORD :　architecture / tools

A whetstone, grinder, or grindstone. A tool used to sharpen the blade of a plane or chisel. Carpenters used a set of ranging whetstones from very coarse, 800 grit to an unbelievably fine 6000 grit, a coarse, rough whet stones were called arato 荒砥, the whet stones midway between rough and smooth were called nakato 中砥, and a very smooth grinding stone was called awasedo 合砥. A blade was sharpened in stages: first sharpened with the arato, then the nakato, and finally the awaseto was used to achieve a fine cutting edge. A flat-surfaced, metal whetstone called kanato-ishi 金砥石, was is used to grind down the back of a blade, and grinding was easier when the kanato was sprinkled with a small amount of emery powder. The arato was made of sandstone, mainly from Oomura 大村 in Nagasaki prefecture, the nakato was made of shale, taken from Amakusa 天草 in Kumamoto prefecture, and the awaseto was slate from Takao 高雄 in Kyoto. However, now that sources of naturally occurring stone have declined, most whetstones are man-made. Special rounded whetstones are also produced to sharpen tools with curved blades like the *marunomi 丸鑿 and the *maruganna 丸鉋.

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