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The ash left from burning plants. Water run through it gives lye.
Obtaining
Usage
Grass or wood alike
Grass, sasa, leaves, vines, bamboo, straw — any of them burnt in a furnace leaves plant ash. What gets burnt has always depended on the place: Okinawa soba used ash from gajumaru and deigo wood, Lanzhou noodles the ash of a desert plant.
Dusting a tatami mat
Put it with a tatami mat and you get one with ash gathered along its edges — for building a room that has been lived in.
Leaching the lye
Put it in the lye tub with a water bottle to get kansui.
As an ingredient
Behavior
Lye reaches past noodles
Lye has long been used well beyond noodles — drawing bitterness from wild greens, setting konnyaku, brewing sake, dyeing with indigo. Edo had ash buyers working the streets and ash markets to trade it. Here it goes two ways: kansui for noodles, and dust for a tatami mat.