Cai Lun, the palace eunuch who made paper cheap enough to replace bamboo
Of the men behind China's Four Great Inventions, only one is known by name, and he did not strictly invent anything. Paper had existed for three centuries before Cai Lun, a Han court eunuch, found in 105 CE a pulp recipe of bark, rags and old fishnets that made it practical at scale.
Before Cai, Chinese writers used bamboo strips for long texts and wooden slips for short ones: heavy, bulky and awkward. Silk was lighter but far too costly for everyday use. Cai's process boiled hemp waste, worn rags, fishing nets and, above all, tree bark, probably mulberry, into a pulp, beat it with mallets, diluted it with water and lifted the fibres out on wooden sieves to dry. The result, called Cai Hou paper, soon pushed the older writing surfaces aside and made him famous across the empire. One popular legend says he got the idea from watching paper wasps build nests.
His career was a study in court survival. Born into a poor family in Guiyang, in today's Hunan, sometime between about 50 and 62, he was serving as a eunuch at the Luoyang court by 75. He helped Empress Dou clear the way for her adopted son by interrogating Consort Song, mother of the rival heir, and her sister, both of whom then killed themselves. When that son took the throne as Emperor He in 88, aged 10, Cai rose to the highest post open to eunuchs, and he came through the emperor's coup against the Dou clan in 92 untouched.
Later he ran the palace workshop, whose ceremonial swords were praised as models of craftsmanship. In 110 the regent Empress Dowager Deng put him in charge of more than 100 scholars producing a definitive edition of the Five Classics, and in 114 he was made a marquis, lord of Longting, a village of 300 families.
Deng's death in 121 exposed him. Summoned to answer for Consort Song's death decades earlier, he took his own life rather than face likely execution. Almost everything known about him comes from about 300 characters in the Book of the Later Han, written nearly three centuries after he died. In China he is worshipped as the god of papermaking; elsewhere he is little known, though his hometown of Leiyang still makes paper.
Source: Cai Lun
