Before Cai Lun improved techniques for papermaking, writing used to be done either on wooden plates and bamboo slips, which were rather heavy, or on silk or cloth, which was too costly, or on hemp paper, which was too coarse.
Cai Lun, a eunuch of Emperor He Di, realized that the paper had to be of better quality as well as cheaper, if it was to be more widely used. He began his research by taking a small step to advance the current technology, which involved beating hemp fibers into a pulp, which was then pressed into thin sheets. He made a finer pulp, but the pulp was not fine enough. Furthermore, hemp, being the chief material for producing cloth, was too costly for papermaking. New materials had to be found.
In his search for a cheaper substitute for hemp that was still as fibrous, Cai Lun experimented with Ink brick. Over 1,800 years old, this ink brick still looks as good as new. recycled cloth, broken fishnets and bark. He put these things into water to soak until they were washed clean. Then he pulped them in a stone mortar. The pulp was then pressed much the same way as hemp pulp was pressed. Paper made out of these materials was much cheaper, but not smooth enough. Cai Lun wanted to obtain a finer pulp so that the paper could be of better quality. He tried putting in lime, hoping this corrosive material would further break down the fibers of the cloth, fishnets and bark. The result was better than expected. Not only was the fiber more thoroughly broken, but the pulp was also whiter thanks to the blanching effect of lime. Cai Lun was excited at his discovery.
However, he found that the paper produced out of the blanched pulp still contained coarse fibers. Furthermore, the lime used during the pulping left small particles in the product. To eliminate these undesirable byproducts, Cai Lun thinned the pulp with water and put it in a wooden tub. He then sank a mesh into the water-pulp mixture for a while, so that the finer and lighter pulp settled evenly on the mesh. The layer of pulp was then dried, and became a sheet of paper that was white and smooth.
Emperor He Di (r. 89-105) was pleased with this new technique. He told Cai Lun to continue with his research and development toward mass production of the improved paper. Cai Lun was made a marquis for his ingenuity, and paper produced by the technique he developed came to be referred to as Marquis Cai Paper.
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