Soaking

The source material for shoji paper is mulberry fiber.
The bark of the mulberry tree is peeled away to the inner white layer, which is soaked in water.
The scum of water-soluble impurities is removed and the fibers softened.
Traditionally, the method of "river bleaching" involved soaking the mulberry bark in the flowing water of a river for two or three days.
After this, it goes through a series of processes, including boiling, removing discolored parts, and beating, before eventually reaching the stage of dipping with a screen to make the paper sheets.