Paste .... why?
Confused about just what the paste is for? You're not alone ...
A paste must be used with the colour in order to hold it on to the surface of the paper and to give brilliancy. The colour, if printed without paste, would dry to powder again. The paste also preserves the matt quality which is characteristic of the Japanese prints. (F. Morley Fletcher)
The medium or binder is paste, made with starch, flour or rice. (Walter J. Phillips)
The starch paste gives a thickness to the pigment which will force it into paper when pressed in printing. It also helps in printing, for the paper sticks to the block better, thus keeping it secure on the block when the back of the paper is rubbed with the baren in printing. (Hiroshi Yoshida)
Paste is the basis of color and must be mixed on the block with the pigment by use of a brush. The process must be done only just before printing, and not previously. This gives substantial body to the pigment and thus secures its uniform application to the block. It should be noted that this procedure is not for the purpose of making the pigment adhere to the paper. (Toshi Yoshida)