Gakashi paper

… Paper that has been made as is is called “raw paper,” while paper that has been processed in various ways is called “ripe paper.” The technique of making watermarks in paper was also invented during the Tang Dynasty and is generally called “watermark paper,” as well as “flower blind paper” and “gakashi.” There are two methods for making watermarks. In one method, a pattern is protruded from the blinds (or bamboo blinds) used for papermaking, and this part becomes thinner to create the watermark. …

*Some of the terminology explanations that mention "砑花紙" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…すき起こしたままの紙を〈生紙〉というのに対し，それに各種の加工を施した紙を〈熟紙〉と呼んだ。紙に透しを入れる手法もまた唐代に考案されたもので，一般に〈水紋紙〉と呼ばれ，また〈花簾紙〉〈砑花紙（がかし）〉という。この透しを造る方法には2法があって，一法は紙すき用のすだれ(またはすのこ)に模様が突出しており，この部分が薄くなって透しができる。…

※「砑花紙」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報